The double bass strings from lowest to highest are
E A D G - the strings are tuned four notes apart. The G sring note on a double bass is written in the top space of the bass clef saff.
It sounds like you might be doing some composing or an assignment for school? I teach and write for sting instruments too. If you have any other string questions you are welcome to ask me and I will try to help - my email is firstname.lastname@example.org