I don't understand your question?
At the bottom of the user profile field manager you'll see Display Page.
Just choose "Edit Profile"
You'll get the Profile Field#
Ie if you add a Sex profile field8
Code:
<if condition="$post[field8]">Sex: $post[field8]</if>
That is saying "If field8 in the profile is populated show Sex: whatever is in the field". "If field8 in the profile is not populated - skip the rest of the code"
Edit: That of course would go in your postbit/postbit_legacy templates.