Bard would likely have some literacy.

More likely would have been taught orally. A traveling minstrel type bard is unlikely to have written music. Learn the song from your master/other performers then adapt as you wish.

We actually have quite a few troubadour “songbooks” from the late middle ages/early Renaissance period, indicating that it was a useful resource for minstrels of the time.

If we’re getting into the Renaissance period, a professional musician would almost certainly be able to read; we have printed music manuals from the period for all kinds of instruments; for example, Arbeau’s Orchésographie is a primer on courtly dance music that we still read today.