Below are examples of the Dorian scale in D at various positions on the guitar neck. These examples use standard guitar tuning (E, A, D, G, B, E open guitar strings lowest to highest).
The horizontal lines in each example are the guitar strings. The lowest guitar string is at the bottom. The vertical lines are the guitar frets, where the numbers of the frets are at the top of each of the patterns. The white notes are the tonic of the scale (the first note). The gray notes are the dominant of the scale (the fifth note).
These scale patterns can be transposed to other positions on the neck to produce other Dorian scales and can also be used for modes of the Dorian scale (i.e., the major or Ionian scale, the minor or Aeolian scale and so on).