I want to know how you became so happy

mai janna chahta hoon ki tumne kaisa bahut khush bane ( why were you so happy = tum kitna khush   kyo  the )  , we  don't use  'Bane'' ( became) word with happy or sad,

I want to be where you live
mai vahaan hona chahta hoon jahaan tum rahte ho

I want to study what you are learning in school
mai vo padhna chahta hoon jo tum school mein seekh rahe ho

I want to go when he starts to talk
mai tab jana chahunga jab vo bolna shuru karega

I want to eat what you are eating because it looks good
main use khana chahta hoon jise tum kha rahe ho kyonki vo acha lag raha hain

I want to understand how you became so smart
main samjhna chahta hoon ki tum kaisa itane hoshiyaan bane

I know why you are here
mai yeh janta  hoon  ki tum  yahaan  kyo ho

I will find who took my money
main usko dhundunga jisne mera paisa liye

I will find out when you will start work tomorrow
main dekhuga ( To see/watch) jab tum kal se kam shuru karoge ,

These are Urdu words. The meaning of these words  are   ''thanks a lot '' Actually  Bollywood songs are mixtures  of different languages like Urdu/Hindi (Hindustani ), Punjabi  and English etc