It's a very interesting expression.So I'm not sure I can give a correct answer.I need before and after this sentence. ウキウキ expresses happy feelings before something happy things is happened that he could expect. ウキウキしている＝I feel happy about it will happen next ( and I know what happy things whould be happend) 俺のウキウキの行方は！？ ＝Where will my happy feeling go to!? I guess, he expected some happy things would be happened next,but it's not happened.So he doesn't know to deal with that happy excited feeling. Or it hasn't been happened anything yet,and he feel ウキウキ for some reason and he doesn't know why he feels ウキウキ. I'm sorry I can't explain well. And this sentence is quite unique expression. It's in my opinion.