I have a 5 year old daughter and she never knew her dad because her dad is a sexoffender and now he wants to be in her life what should I do

First its not a good idea to piggyback your question on another thread. This can lead to confusion. So I've moved your question to its own thread.

There is little you can do. Is there an order for visitation in place? If not, you tell him to go to court for visitation and then fight it in court. Without knowing the level of offense we can't tell you the chances of his getting visitation.

He's been in prison? Depends on what the sex-related offense was (did it relate to abuse of minors?), you might want to insist on supervised visitation.

Did he do something sexual with your daughter ? I will assume he was arrested, convicted and put in prison.

Sex offender can be someone who raped a grown women, had sex with a child, or maybe had sex with a 16 year old.

So unless you can prove he is a threat to HIS child, he will get visits, and even if proved a threat to the child, he is very likely able to get court supervised visits.