A C♯ Major (C♯) chord contains the notes C#, G#, F. It is built from the major formula 1 - 3 - 5, with C# as the root.
Should I call this C♯ or D♭?
Whichever the key signature asks for. The two names point at one pitch and one fretboard shape, so nothing you play changes. Music written with sharps will say C♯; music written with flats — which is most of it, since D♭ major needs five flats against C♯ major's seven sharps — will say D♭.