The notes EF and BC are always one semitone apart (one fret). All other notes are a tone apart (2 frets). Sharps (#) and flats ( b ) are found between the notes that are a tone apart.
This scale is called the chromatic scale and contains all the #’s and b’s possible. C sharp (C# ) has the same position on the fretboard as D flat (Db ). They are the same note but can have different names depending upon what key you are playing in. The same applies to D# /Eb , F# /Gb , G# /Ab A# /Bb . These are called enharmonic notes. The following diagram includes all these sharps and flats.
These note positions are important to remember because they are the basis for tuning your bass to itself.