AdminCp -> User Profile Fields -> Add new field
enter the options, make it required upon registration.
AdminCP -> Templates & Style manager -> postbit templates -> postbit(or postbit_legacy)
Find:
Code:
<if condition="$post['usertitle']"><div class="smallfont">$post[usertitle]</div></if>
Add above or below
Code:
<div class="smallfont">$post[fieldX]</div>
Where X is the number of the field that gets automatically assigned.