Related to this post: If the Earth were a smooth spheroid, how deep would the ocean be?
Consider ocean waves in the middle of a large ocean. They are being powered by the wind, but also lose energy due to viscosity, breaking and similar factors. Since the timescale for a wave changing is much smaller than the timescale of it crossing an ocean, for all practical purposes they already experience an infinite ocean.
A featureless ocean world would presumably have many somewhat constant wind systems that could add a lot of energy to wave motion, but with an absence of shores to break on these energetic waves will just keep on going with an amplitude where the average energy gained and lost are equal. Since even a powerful tsunami is nearly invisible in deep water, the ocean world would look relatively calm with merely a lot of ocean swell.