To be annoyed someone has lifted some of my work and used it in a presentation without at least asking?

I'd definitely mention it but keep it positive - e.g. glad to see someone has found my work useful and used it in their presentation, albeit missing a lot of the background content. You could then offer to support whoever used it so that they understand it in more detail.

Years ago as a junior engineer, I once had a training meeting with a manager in a different department who was showing me some work that their more senior engineers had done to demonstrate what their department did. I was rather surprised to see my OWN work on the screen where I'd had an idea for something a year before. The idea didn't go anywhere but the person I'd spoken to about it clearly liked it had had then passed it off as their own work!!

I let the manager know that I was already familiar with the concept as it was MINE, and after a few probing questions from the manager he was satisfied that it was indeed my work and not this other persons. It's nice someone rated my ideas, but it would have been polite to include me or at the very list credit me for the work!

Quite frankly, there's a load of nonsense being quoted about copyright & IP on this thread.
To re-iterate some earlier posters, the work was produced by OP on company time, OP was paid for it by the company to create it & the IP and any copyright is owned by the company.
I've been involved in literally hundreds of presentations, reports and proposals over the years, as lead, contributor or reviewer. Not a single one has ever credited an internal contributor on the material itself. None of the contributors expect it, it's just not the done thing. They are getting paid for their time. The only time people / companies get mentioned in the document are where it's either a customer quote to support a bid or an extract from a 3rd party report like Gartner.
This is business document, not a university / academic research project, where references / credits are expected.
However, what is important here is that people are recognised for their contributions. The bare minimum should have been a courtesy note to the OP saying that this material has been forwarded onto them, thanking them for creating something useful & mentioning that they will be using it in their work (n.b. it's an inform, not an ask). OP can then use this as credit for their next review etc.
In this situation, my comms to my line manager would be along the lines of "hey boss, just a quick note to let you know that fred found the work I did on xxx really useful & has used it in their training material. I'd be happy to work with them / you on future initiatives to ensure the best value is made of this work as I'm really pleased with how xxx is being received". You'll get loads more brownie points than kicking off about it.

I once helped out another organisation interview for my position in a different area. We had an interviewee who presented on how they would set up their area and had totally ripped off our work that I had personally created from our website. They didn't cite us at all just pretended it was their work. Needless to say they didn't get the job.

I was and would be annoyed too, I think I'd speak to who presented and ask them to cite you.

This happened to my husband who wrote with English spelling for an American software company. They haven’t even changed the name of the file which references his first name and his home computer in it.

He’s exactly like you. Kinda cross but ..

I’ve had this happen to me and I get how annoying it is. No matter what the copyright/rules of your workplace, it’s common professional courtesy to acknowledge that you’ve used the work of others. As you say, you have no issue with people using it but if it’s used without proper acknowledgment then people can start to misdirect credit which can be a bit sticky. Hopefully a friendly chat will work.

Thus the worker could theoretically plagiarise themselves if they used even part of their work in another context or be sued for intellectual theft or copyright.
Not quite, there is legal provision for the use of skills that may result in something similar being created during innovation. It's a tricky area of law in IT and engineering particularly! Imagine hiring an engineer who built a firewall to build a firewall... they learned stuff the first time around so bits of it may be really similar. They can't copy, they must not try to copy, but elements of similarity due to that being how that individual's brain can design a firewall are an inevitability.

Presenting work as the author's own is completely different than reusing internal company training resources. Training courses are frequently made up from many people's input and are not created just for evaluation purposes. What you describe is deliberate misrepresentation, what OP described was someone delivering a training course.

There is often a bit in your contract that states that anything created as part of your job is the property of the employer. For example, training materials and presentations.

The worker who creates them can’t take them with them when they leave, sell them or share them with others. Thus the worker could theoretically plagiarise themselves if they used even part of their work in another context or be sued for intellectual theft or copyright.

THis happened to me in a slightly different context. Someone used my work and presented it as their own for their assessment - at which I was present. As it happened so was the person who assessed me in the past.

There was an uncomfortable silence following the reminder by the assessor, to the audience of other trainees and supervisors, that all work presented should be orginal and not that of others.
And I wasn't flattered. I was furious!

Legal advice!! This is just mumsnet, you need to present your actual contract and details to a lawyer.

Particularly if you are giving healthcare input without the latest training, and it's a different industry where your employer's professional indemnity insurance may exclude this.

I would put your signature on all your work and make it view only so it can’t just be copied. Use the pp’s words re thanks but in future please reference me so people can contact the right person etc.

If this is about ensuring the wrong information isn’t getting out there you probably need to be discussing how training is done organization wide. Having authors gatekeep the materials they create is a poor solution for an organization as people move on. That they had a someone presenting on information they didn’t understand properly seems to be more the issue here, not that they used your material.

This.

It is never ok to share work without due credit to the authors. Surely everyone who has ever completed an essay knows this? It is so wrong on so many levels to pass work off as your own.
And if you are credited to do training you should be especially wary of this.
I agree if doesn't look like it's done maliciously, more naivety, but even still, you need to make management aware of this so the correct credits are applied.

If you leave it, it will grow arms and legs, and as you say, there's a danger that further members of the organisation will think it's YOU copying THEIR work

In your OP you said "I have a niche knowledge base that is not common for where I work and I have been working on projects bringing some of my expertise into the field. Part of this was a training suite which has been going on for well over a year."

Now it's suddenly "completely unrelated" and no expectation to "share my knowledge". Not making much sense here OP. I'll repeat again, you need some legal advice here to understand your position.

This

Generally work produced in the course of employment belongs to the company and not the employee personally. The company can use and adapt work produced by any employee in anyway they choose.

The only issue in OP’s situation would be if the presenter said they had produced the work personally.

I hope it is the only example of the plagiarist doing this without normal courtesy.

I don't think they needed to ask, but there should be a citation. People use people's work all the time. I use charts from HMRC, quote blogs and articles no point writing your own if someone has already done the work. But you need to acknowledge that in the presentation. I wouldn't know who to ask in HMRC for example, just add a citation.

I think I'd have drawn attention to the fact it was my work at the presentation.

I can choose whether to share skills and knowledge I gained elsewhere or not.
Unless you were taken on as an unskilled person with no experience required on the job spec, you might find iyour experience was a factor in why you were hired, and that support is required as part of your role. I really think you need legal advice before you take this attitude to your workplace, you need to be crystal clear about what your contract says, and what that actually means, before you start stomping your feet about your perceived rights.