Here are the top ３ ways to say WHAT in Japanese
1: Nani: なに: What
2: Nan desu ka: なんですか: What
3: Nan darou: なんだろう: What
Also if you are in Kansai Region (the Southern Part of Japan where Kyoto, Osaka and Kobe are located) and speaking Kansai Dialect (Kansai-Ben) you’d say
NANYA!!! なんや！This is saying “what” in a friendly way.