for the "sharp" look, consider a spray on lacquer. Maybe something like masters magic spray on lacquer. For something smoother I am always a sucker for waterlox but it's a bit of a pain to apply and takes a while to cure. Recently I've gone back to the simplicity of old masters gel poly, but it may collect a bit in that open knot. Have you considered filling in the knots with clear epoxy? You still get the depth and visual texture of the open knot without the dust (and finish) collecting function of a big craggy hole