So far, everything in this book has used only the key of A. This was because it is important to be able to play all over the fretboard in whatever key you are playing in. However, not all music is written in the one key. It is important to be able to play equally well in all keys. The first thing to do is to memorize the names of all the notes on the fretboard.
Here is a diagram showing all the notes up to the 12th fret where they begin to repeat.
A good way to learn all the notes is to take one string at a time. Call the "in between" notes sharps as you progress up, and flats as you go back down.
The fingering is not important here, just the note names.
The dots on your guitar are good points of reference. You can use them to help the memorizing process.
Next, pick the name of a note at random and find it as quickly as possible. When that becomes easy, move on to the next string.
Another good thing to do is to find the same note on every string. Usually a note appears twice on each string unless it is at the eleventh fret - except for guitars with 24 frets.
One last way to learn the notes is to go across each fret. Again use sharps as you go higher in pitch and flats as you go down.