Scales to Play Over Dsus4
Every chord is a subset of several scales: any scale that contains all of a chord's tones fits over it. Pick a chord to see the matching scales from its own root, the major keys the chord belongs to, and full fretboard diagrams for every scale on guitar.
A Dsus4 chord contains the notes D – G – A. Any scale that includes every one of those 3 tones fits over it — from the root D, that means D Major, D Natural Minor, D Melodic Minor, D Harmonic Minor, D Minor Pentatonic, D Blues, D Dorian, D Phrygian, D Mixolydian, D Dorian Bebop, D Mixolydian Bebop and D Spanish. Start with the first scale listed: it is the most common choice, and the others color the same chord tones differently.
Dsus4 is also diatonic to 5 major keys: A# major (relative minor Gm), C major (relative minor Am), D major (relative minor Bm), F major (relative minor Dm), G major (relative minor Em). In a song from one of those keys you can also solo with the key's own major scale or its relative minor pentatonic across the whole progression, not just this chord.