I’d imagine that the level of knowledge required depends mainly upon two things:
Do the company manufacture in-house? If so a higher level of knowledge may be required as you will have to do everything (including all the little corrections/alterations that an external manufacturer might do without telling you about it just to get the job done).
Will you be the only person there responsible for the molded plastic parts? If there is going to be a more senior member of staff who also works on molded plastic parts they are most likely expecting to offer some on the job training. If it’s only you, you’ll need to hit the ground running.