In bahasa you can say "What are you thinking about?": - Apa yang kamu pikirkan? - Kamu lagi mikirin apa? (informal) The answer "I was thinking about my holidays." : - Saya memikirkan tentang liburan saya - Aku lagi mikirin liburanku (informal) In bahasa, we can choose to use formal form (baku)-> sound like text book or informal form (tidak baku). But mostly used informal form if we talk to friend or just for daily use. Informal sentences (kalimat tidak baku) in bahasa have many variation based on the culture and environment. So sometimes difficult enough for foreigners to understand. I hope this helps

Hello. In Bahasa you can say "apa yang sedang kamu pikirkan?" but that's very formal. If you want to say it informal, you can also say "lagi mikirin apa?" you can put "kamu" before "lagi" if you want but usually I don't. It's up to you. And to answer it formally, you can say "aku sedang memikirkan liburanku" you can use "saya" or "aku". But maybe it's just me, I would use one of them in one sentence. Meaning if I use "aku" then I will say "liburanku". And if I use "saya" I will say "liburan saya". It's okay for both of them. But I don't really like to mix them in one sentence. Hopefully my answer will help you.