Let's observe the intervals: between the root and 2nd (9th) there will always be a major second interval (one whole step, 2 frets); between the 2 and 3 there will always be another major second interval; between the 3 and 5 there will always be a minor third interval (one and a half steps, 3 frets) and between the 5 and root there will always be a perfect fourth interval (2 and a half steps, 5 frets). Memorize these intervals as you will be able to apply them in all the various string layouts of the add 9 arpeggio.
This is a layout of a root position Add 9 arpeggio where the root is an open string and the form is 4 notes-per-string.
Example two shows all six arpeggios where the open string is the root. Not only can you play this 4 notes-per-string form with slurs and tapping but you will see demonstrations of how to apply legato slides and bending to this arpeggio form.