Learn Dutch: Hallo, ben je thuis? - Hello, are you home?

To ask a yes/no question in Dutch, you swap the subject and the verb. So the statement je bent (you are) becomes ben je (are you). Notice a special Dutch spelling rule here: when je or jij comes directly after the verb, the verb drops the -t at the end.

Could I say ben jij thuis instead of ben je thuis?

Yes, you can! Both je and jij mean "you" (informal singular). je is the standard, unstressed version used in everyday speech. You would only use jij if you really need to emphasize you (for example, "I am at the office, but are you at home?").

Why is there no word for "at" before thuis?

The Dutch word thuis actually translates to "at home" all by itself. If you just want to talk about a house as a physical building, you use the noun huis. Because thuis already includes the idea of being at the location, you don't need to add an extra word for "at".