I cant finish Kagains quest no matter what i do.
It never triggers any dialogue and i cant find any corpse holding that item
what should i do?
all over the map nothing triggers the dialogue.

What area are you in? According to the walkthrough from NPC Project, if you have Kagain in party, when you enter area FW2800 (or AR2800 in original BG; this is the "Coast Way" area where you run into Elminster the first time, early in the game), he should initiate dialog and tell you to head east. There should be some bandits over that way. After you have killed the leader he should talk again. There should be a corpse in this area with a fibula, which you're supposed to pick up.

Are you in area FW2800? (You can check area and coordinates with the X key) You're not finding any bandit?

It is possible to properly complete the Kagain quest. Move from Beregost to the forested area between Beregost and The Friendly Arm Inn, the one directly north of Beregost. On this forested map there are two Raided Caravans. Now, move with Kagain to the Raided Caravan to the east. If you didn't kill the bandits here when heading to Bergost before then you will need to kill the bandits now. Then move close to the bodies of those from the caravan that were slain by the bandits and Kagain will then identify one of them as being the son of Silvershield. Kagain then announces that he'll be a wanted dwarf now and so he'd like to stay with the party to hunt bandits to get revenge upon them. Regardless of whether you take him with you, or kick him out of the party, he pays you the gold pieces he promised per head of the party. Then the quest is marked as complete.