How can you make a npc sit on a chair?
Ask him to sit down.
Sorry, couldn't resist. :D
It's likely a scripted animation on a loop. Or somesuch. To be frank, I know very little about animations...
same here thats why im asking.
Almost certainly it's a looped animation. You could try adding a script to the OnHeartbeat slot of the .utc file, something like:
void main()
{
object oNPC = GetObjectByTag("object_tag");
AssignCommand(oNPC, PlayAnimation(ANIMATION_LOOPING_SIT_CHAIR, 1.0, -1.0));
}