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.
Another good song to remember for this is that very first bit of “Cant stop” by the red hot chili peppers!