A Kansai-dialect way to ask "what kind of thing" or "which one" (equivalent to standard どんな(の)). Used to ask about the type or nature of something.
新しいプロジェクト、どんなんなん？
What kind of new project is it?
そこの店の料理、どんなんやった？
What were the dishes like at that restaurant?
どんなん欲しいか教えてくれる？
Can you tell me what kind you want?
どんなんでも構わへんよ、とにかく早くして。
I don't mind what kind it is — just hurry up.