Here is a fretboard diagram of all the notes on the bass. Play the notes on each string from 4th string is an E note and the note on the 12th fret of the 4th string is also an E note but is one octave high-pitched open note to the 12th fret. The note on the 12th fret is one octave higher than the open note.
One more useful way of learning the notes is to go across each fret. Once again, use sharps as you go higher in pitch and flats as you go back down.