Where to capo for D Lydian
Put the capo at fret 2 and play D Lydian using C Lydian shapes. That is the easiest of the eight positions ranked below, and it is what most players reach for. Against playing D Lydian open, it drops the mean difficulty of the key's seven chords from 4.3 to 3.4 and gains 5 ringing open strings.
You want D. Capo 2 and play in C.
All eight positions, ranked
Each row transposes D Lydian down by that many frets to find the shapes your hand would actually make, then scores the best voicing of all seven chords — fewer fingers, less stretch, closer to the nut, fewer muted strings. Lower is easier. Standard tuning (E2 A2 D3 G3 B3 E4).
What you are playing
The seven chords of D Lydian are D, E, F#m, G#dim, A, Bm, C#m — the ones the ranking above is scored against. Their diagrams are on the D Lydian key page.