There is no definitive answer to this question as there is no known way to measure the depth of an ocean in the universe. However, based on our understanding of physics and astronomy, it is believed that the deepest ocean in the universe is likely to be located within a black hole.
A black hole is an extremely dense region of space where gravity pulls matter inward towards a central point known as the singularity. Once matter crosses the event horizon (the point at which escape from a black hole becomes impossible), it can never return to our Universe. As matter falls into a black hole, it heats up and compresses, eventually becoming so dense that its gravitational pull becomes overwhelming even for light. This means that anything inside a black hole - including an ocean - would be effectively cut off from the rest of the Universe.
The depth of an object within a black hole can not be measured directly, but scientists have theorised that it would be incredibly deep due to the immense gravitational forces at play. It has been estimated that if you were to fall into a supermassive black hole (such as those found at the centres of galaxies), you would reach speeds of up to half the speed of light before being pulled apart by tidal forces and ultimately crushed by gravity. This means that any oceans located within a black hole would be under immense pressure and incredibly deep - potentially infinitely so.
While we may never know for sure what lies at the bottom of these cosmic oceans, one thing is certain: they are unlike anything we have ever seen or could even imagine here on Earth!