Well I would like to find out if I have a daughter? My ex girlfriend told me that I do but she cannot prove it with legal documentation because she said she had a closed adoption. What can I do to see if I really do have a daughter? I would like to get legal documentation.

I cannot see how you can do it.
Firstly-you have never established your rights as a parent
Secondly-After "Baby Jessica" and "Baby Richard" cases the legislation was changed and generally the Courts are very reluctant to re-open a case if adoption was finalized by court decree.

First--how old would the child be?

Second--what state? Some states can take your rights if you don't register on a putative father list WITHOUT contacting you.

Third--if the child was adopted, you don't legally have a child. Period.

Fourth--I'd ask her to show you her relinquishment papers. Almost NO child goes into a complete closed adoption in today's society.