How well should I know the fretboard before moving to the C major scale?
You don't need much fretboard knowledge at all to get started with the scale.
You only need to know the names of the strings, the tuning relationship between the strings, and that one fret = 1/12th of the western chromatic scale -- and, therefore, that any two tones 12 frets apart is an octave interval (notes with the same name).
After that, all you need is to be able to press one finger on the board to sound a note.
Fretboard knowledge starts with learning where to place the C major scale in the sea of frets that is a guitar neck. Learn those intervals one string at a time using one finger, as all of Tomo's videos explain. Then learn how adjacent strings are related. Wash rinse repeat.
Once confident with the intervals of the scale on each string, you can move on to more advanced fingerings in later videos.
Everything else, all scales, modes, chords, and harmony is derived from the relationship to the C major scale. So learn it perfectly and have fun while doing it!
Here is Tomo's comment:
"Thanks so much for subscribing to my Guitar Wisdom. Don't overthink this! Learn the C Major Scale on each string over a few months. Then, learn to play F everywhere on the fretboard. Learn the Major scale in another key -- maybe F. Take your time and learn everything deeply."
Thanks! The new videos on triads helped. I have alot of work to do! ha