Triad chord ear training
There are four main types of triad chord: major, minor, augmented and diminished. Start out by making sure you’re solid on major versus minor, and then introduce the other two triad types.
Once you’re familiar with the characteristic sound of each type of triad, you can improve your chord skills by working with triad inversions, so that you can recognise not only the type of chord, but also which inversion you’re hearing, all by ear.
Guitar chord ear training
Once you have the basic listening skills for chords, it’s time to connect them with your guitar. This involves working on similar triad chord recognition exercises, but using your instrument to play the chords (or recordings of guitar triad chords).
You can learn about triad shapes on guitar, and then practice by yourself or ideally with a friend, to develop and test your ability