When you learn a song by ear, you'll know how each note of it relates to the key (which is the "home" note, and the one that the song might end with). You also know where the half-steps are in the scale. These are basically enough to know your solfège/solmization syllables for that song. Note names and perfect pitch are irrelevant because most of the time you'll be playing fretted notes, so just shifting your hand location on the fretboard lets you play different pitches - the actual "note" pitch is arbitrary. Notes played unfretted (that you can't just move around) are rarer, so you can always think of them as falling outside the pattern and learn them as such.