Learning the names of the notes on the ukulele takes a bit of work but is well worth the effort. It will improve many aspects of your playing from recognizing chords, playing in different keys, sight reading, improvising, and much more. The worksheet below will test your knowledge of the notes on each string.
Take your time and try to memorize one string at a time. Knowing how note names move with whole steps (2 frets) and half steps (1 fret) up a string without sharps or flats is helpful.
For instance, starting from C the notes move like this: whole-whole-half-whole-whole-whole-half
C D E F G A B C
The half steps are between the notes E and F as well as B and C.
Try to cover a new string each week and see if you can have the fingerboard memorized in a month!