The Major 2nd Interval

The Major 2nd Interval is the same as a Tone, a two fret step on the fretboard. It's a VERY common melodic interval and one you should easily recognize!

View the full lesson at The Major 2nd Interval | JustinGuitar

I think there might be a diagram missing here for the interval on guitar.

The diagrams are indeed missing

You don’t really need a diagram. The ascending major 2nd interval is two frets higher on the same string as the first note you play.