I think nobody wants to be friends with you.
More natural as : "I don't think anybody wants to be friends with you.")
Nobody wants to be friends with you
Nobody skips school today.
(More likely to be: "Nobody is skipping/has skipped school today.")
The '-s' is the third person singular ending of the verb in the present simple. 'Nobody' is singular, and is therefore followed by verbs in the present tense with this ending.