Regardless of the type of finish, gloss is a function of surface smoothness. A film type finish can achieve smoothness by filling in larger gaps.
The surface finish of the wood (final sanding grit, fineness of scraping), and the type of grain - open like oak or tight like maple - plays into it as well. Getting the desired gloss level is a matter of balancing bare wood surface finish and finish film thickness, as well as the sheen of the finish type used, and/or buffing waxing (which simply smooths the surface and fills in gaps with wax).
Watco DO is a film finish (varnish) - it will dry hard on a nonporous surface. Adding more coats will increase gloss. There is a simple way to reduce the # of coats - leave the DO on the wood, and keep it wet (add more as solvents flash), then wipe off. You can do this for as long as you want, more than an hour. If it gets too gummy to wipe off, just add a bit more - it will thin things down enough to allow wipe off. Difficult to screw up, really, unless you walk away and allow it to really start setting up.
Years ago, after playing with oils and varnishes and DO’s and whatnot, I found plain old minwax poly, thinned 1:1, and applied as described above, did the same thing as DO but more quickly. I’ve settled on minwax helmsman spar, as it has more oil in it for long term flexibility and has a bit darker color, which provides just a bit of grain enhancement.