A student can have any motto he or she likes. A motto is a personal thing.
Take a look at the advice I give in the article on how to find your motto and you will soon come up with a motto.
Your motto may come from something your teacher says, something you read in a book, something you see online, on TV, or in a movie, or something you hear in a song. When you hear it, you will recognize it. Your mind will keep returning to those words.
As I said it the article, keep it short and phrase it as a command. You want words that will inspire you to reach your goals and achieve what you want to achieve. It could be as simple as "Do My Best!" But, I don't want you to take my suggestions. They are meant only to serve as an example. Your motto is personal to you so it must come from you for it to be meaningful and to work for you.
Some years, when I am trying to find my annual motto, It is hard for me to choose from all of the ones that spring into my mind. Some years, I can't even think of one. Just when I think I will have to continue with last year's motto, the new one pops up in my mind.
I know you will find the motto that is right for you.