C# - di, D# - ri, F# - fi, G# - si, A# - li
Db - ra, Eb - me, Gb - se, Ab - le, Bb - te
The first way to learn the fretboard is to learn the notes on a string. For example isolate the D string:
If you know the diatonic/chromatic sequence of notes then you could start from the open string adn count down till the 12th fret and name its note.
However, this method does not help you memorize the notes in the higher positions. You have to learn to recognize the fretboard vertically. For example isolate the 5th fret:
Do this for all the frets. I recommend learning the frets in the following sequence:
0, V, X (0 accidentals, 6 natural)
III, VII (1 accidental, 5 natural)
VIII (2 accidentals, 4 natural)
I, II (3 accidentals, 3 natural)
IX (4 accidentals, 2 natural)
IV, VI (5 accidentals, 1 natural)
XI (6 accidentals, 0 natural)
I will give you two pictures of the fretboard with all the notes on them. The first has the natural and the flats:
and the second the naturals and the sharps:
Copy and enlarge those diagrams, then cut slices for each fret and memorize the sequences.
Have fun!