To think new employee should know what to do

[user1498253950]

AIBU to think that by the end of 4 weeks in a new job someone should be able to most of what is on their job description? Basically, colleague left and I was left covering that job (and doing my own job). New person started 4weeks ago and I am still doing at least 50% of their job with no payment and no support.

It depends on the job. Handover and training are different things. Some cyclical tasks only occur once per week/month/quarter/annually, but completing ½ of someone elses work & training without support or payrise sounds unreasonable to me.
Does your job description include training colleagues ? If so its up to you to sort out. Are you training when you should only be handing over? Do you think the new employee would benefit by going on some training courses? If yes stop and tell your line manager. Whatever the answers are you need to tell your line manager of your difficulties - don't forget its their job to support you & help sort your work problems out. It may be that they have recruited the wrong person or you also need support in certain parts of your job (i.e. training).