How can I find out my nationality ?

You’d have to do research on all the last names of your family to find out where everybody was from….really though you’re trying to find your heritage, your “nationality” is dependent on where you were born. Eg, you’re American as you were born here.

But, I’d strongly suggest making a list of all the surnames you can find and then researching those….you can use something like ancestry.com, or a similar website, that will help you in your research after you talk to all the members of your family (also see if they have already done the work, if they have, it’ll save you a lot of time).