Hard to answer without knowing the band.

I can’t answer that directly because you didn’t say which band.

Every band is different. Some have zero guest musicians. Some have dozens. You’re asking for the one song that features a guest—that could be The Beatles (“Come Together”*? no, no guests) or Nickelback (plenty). Without a band name, I’m guessing.

If you have a specific band in mind, drop the name and I’ll find the answer. Or just check their Wikipedia discography—that usually lists guest appearances.