Here are the possibilities for different intervals in D Dorian on the D and G strings.
Of course, if you have exceptionally long fingers, or a high tolerance for pain, you’ll be able to play 7ths, octaves and unisons on two adjacent strings, but for us digitally compromised individuals, we’ll be sticking to a range of 2nds to 6ths.
And even that might bring you to pray for granny’s cod-liver oil.
Keep trying, though :)
Move a particular dyad through the scale until you’re familiar with the fingering and sound.
Remember you can use any of the open strings in this particular key. Try adding the open B and E.
Sometimes you get nice clusters. E.g., if you play C and F on the 10th fret [on the D and G strings]. Then add the open B and E you get a clustery chord.
That’s a nice thing about these linear interval things: you can just move them up and down the fretboard and see what takes your fancy.