OP, a quick google revealed that a toolbox talk is a short presentation to the workforce on a single aspect of health and safety.
https://www.hse.gov.uk/construction/resources/toolboxtalks.htm
HASAWA 1974 is the Health and Safety at Work etc Act 1974. As for what is the hardest part to enforce, if you have no understanding of the act itself, read it from cover to cover and find articles on it. You can ask ChatGPT this question.
I don't know if your current and desired job involves health and safety but this could be one area to beef up on.
The trick with interviews is to know a little about everything of any and all the topics that could come up and prepare a little speech on each question that could come up. I usually end up with 2 A4 sides of notes which I rehearse the day before so it sounds smooth and credible.
For example, in my field, Russian sanctions are very topical. If I was going for an interview, even if I know zilch, part of the prep involve researching what they are, the key issues and latest developments and implications for the sector. I make notes, like I was in school, and rehearse a quick elevator pitch to be able to talk about it in 2-3 minutes. I might get out of my depth quickly if the interviewer probes, but at least I started strong and sound knowledgeable. And then explain how you would plug any gaps in your knowledge. Tick.
I know this is in hindsight. Which is not to make you feel bad. I have a lot of experience going for jobs that are just that little out of my experience and seniority. This is how I blag my way through. I am not super confident nor good at making things up on the spot and so my prep is to research and rehease.