@401Blues Learning (not memorizing) the fretboard is something that happens over time and with repetition. Notice, I said learning, not memorizing.
The board is like a map, you just have to learn how to read it. Once you’ve pinpointed the location of a few notes, you can easily navigate to neighboring notes… you just have to know the direction and distance you have to travel to get there.
I’m attaching a graphic I made when I first started playing (I also made one for 5 string if you want it). Think of it as a roadmap. Use it as a study guide but don’t try to memorize it. You’ll soon recognize some of the patterns. Just learn things like: if you are on the 3rd fret of the A string ( C ), for example, one string up is F (4th), one string down is G (5th below), two frets up and two strings up is the octave, the octave is always one string above the 5th, etc. This same pattern applies no matter what key you are in.
Also notice that each fret follows the same pattern of 4ths: C, F, Bb, Eb, Ab, Db, Gb, B, E, A. D, G. For example, Bb is always one string above F. B is always one string above Gb. D is always one string above A, etc.
Once you are able to remember the location of a few notes, getting to other notes becomes a piece of cake, once you understand the sequence … and then eventually you’ll remember the location of those notes as well.
Practice practice practice. Study study study. Enjoy enjoy enjoy.
