dokučiti

1. to grasp; to figure out; to comprehend
   Nikako ne mogu da dokučim šta je hteo da kaže. — I just can't figure out what he meant.
   Konačno je dokučila zašto program ne radi. — She finally figured out why the program wasn't working.

Often used with a negative: "ne mogu da dokučim" — "I can't work it out".