iskazati

1. (of feelings, attitude) to express; to show
   Želim da vam iskažem zahvalnost za svu pomoć. — I want to express my gratitude to you for all the help.
   Građani su iskazali nezadovoljstvo na protestu. — Citizens expressed their dissatisfaction at the protest.
2. formal (of data, figures) to state; to report
   Firma je prošle godine iskazala veliki gubitak. — Last year the company reported a big loss.
3. (iskazati se) to prove oneself; to distinguish oneself
   Mladi golman se odlično iskazao u finalu. — The young goalkeeper really proved himself in the final.

In the sense "to prove oneself" it takes se: iskazati se kao lider, iskazati se u poslu.