How would you term a person who gives you a job opportunity and then reminds you to be grateful that he's given you that opportunity....
If the job opportunity were given at some risk or sacrifice to the giver's interests, then I would consider the giver's reminder to be prudent; otherwise, I would consider the reminder to be an indication of insecurity or of gracelessness.
I think this is a good question.
I don't have a noun for such a person, but the action they doing is holding it over you, or holding it over your head.
God - That Jim, he got me a job at the company he works at, and now he's forever holding it over me, he's always asking me to babysit his kids and mow his lawns, when will it end?
Best definition I've got for it is from urban dictionary:
Hold it over your head - This term is for when you do a favor for someone,then use that favor to to taunt or guilt them.You try to keep this status over them as long as possible until you can cash that mother fucker in on something good.