If you want to learn the notes on your guitar, it helps to know a few shortcuts. (If you're completely unfamiliar with the notes on the fretboard, you may want to start here first) There's a group of notes called the perfect harmonies - we're going to use these to help us figure out the guitar notes quicker than we could with straight memorization.
The perfect harmony notes are the I, the IV, and the V. We'll look at the key of A, where A is the I. If you start on the A on the 6th string, 5th fret, then you just go straight across to the 5th fret of the adjacent string, the 5th string, and you have D, which is the IV. From there, two frets further up the fretboard you'll find the V, which is E.
A = I = root note
D = IV = the fourth
E = V = the fifth
A = VIII = the octave
We can apply this same pattern anywhere you find an A. Take the 12th fret, 5th string for instance. That's your A, one string down you find the IV, and two frets up, you find the V.
Now, you can use a pattern to find the octave of the A too. For that, we go down two strings, and up two frets. The exception to this is when the 2nd string is involved. If your pattern lands on or crosses that B string, then you need to add one more fret. So the new pattern becomes two strings down, three frets up.
With this octave pattern you can very quickly figure out notes in the middle of the fretboard that you may be less familiar with. Most people learn the notes on the 6th and 5th strings first, because of bar chords. Well, the 1st string is identical to the 6th string, and that just leaves the 2nd, 3rd, and 4th strings. If we use the octave pattern, starting from the strings we know, we can cover those remaining strings, no problem.
Knowing the perfect harmony box of I, IV, V, VIII can help you in many ways, from finding chords located nearby, to giving you ideas in your solos, and also for bass players too!
Learning all the guitar notes is great, but you don't have to use straight memorization. Using a pattern like this can really help cut down on the brainpower needed to remember where all the notes on the guitar are, and it takes some of the pressure off too.
Now, go learn some notes!