Another valuable exercise for improving your knowledge of the fretboard is to find all possible octaves of any given note. Remember that an octave is the distance between any note and its next repeat at a higher or lower pitch.
An example of this would be the note C#, which can be found at the 9th and 21st frets on the sixth string, the 4th and 16th frets on the fifth string, the 11th fret on the fourth string, the 6th and 18th frets on the third string, the 2nd and 14th frets on the second string, and the 9th and 21st frets on the first string. These positions are shown in the diagram below. Practice choosing notes at random and finding each one in all possible positions, until you are confident you can instantly find any note in any position.
Knowing how to find higher and lower octaves of notes is useful in many ways. You may wish to repeat something you have played but make it sound higher or lower than the first time it was played, or you may play something and think you have the right notes but it sounds too high or too low. Another situation where this is useful is if you are playing call and response with a vocalist or another instrumentalist. You may know which key they are in and what note they are starting on, but you also have to find which octave they are in as well.
The example below shows a phrase played in different positions on the fretboard and also in different octaves.