No submarine present in the WWII period could have located Titanic. Neither could, in all likelihood, any military submarine contemporaneous with Ballard's discovery of her wreck. Titanic's wreck lies at a depth of 12,415 feet. WWII submarines were not constructed to survive dives to anywhere near this depth. To survive the crushing pressure at great depths requires a thick, strong, small hull. For example, the Trieste, the first submersible to visit the Challenger Deep, had a hull 5 inches thick. Trieste also had a spherical pressure hull, which withstands pressure much more easily than the classical cigar-shape of the typical military submarine. Building a submarine with a hull so thick would cut massively into internal volume. The internal hull of Trieste was just six feet across - little space for her crew to do much more than sit.

Military submarines never need to dive so deeply, so engineering them to survive such depths was unnecessary. This was especially true for those of WWII, where the diesel electric submarines used spent much of their time on the surface. After WWII, the British used crane ships to test the crush depths of several of their classes of submarine, in order to confirm their theoretical predictions. HMS Varne, a U-class submarine typical of British subs of the time, was crushed at a depth of 877 feet, just 7% of the depth where Titanic lies (EDIT: This is possibly incorrect, due to a typo in my source. Varne may have been crushed at 576 feet instead). Cold War submarines couldn't do much better. In August 1984, the one Soviet Mike class submarine set a record by diving to 3,350 feet, just over a quarter of the depth of Titanic. While the Mike was some distance from its crush depth, the crush depth was almost certainly less than the depth of Titanic.

No, for the simple reason that the Titanic lies at around 12000 feet of water. The crush depth- the depth at which water-tightness gives way- of most WWII submarines was under a 1000 feet. The submarines used to explore Titanic are special deep submersibles designed to operate at these depths. Not even present-day attack and boomer submarines can dive to these depth; although the crush-depth of modern submarines is a closely guarded secret, the best guesses peg them at 2000 feet. Deep-diving research submarines first emerged in the 1960s as part of a larger cooperation between the US Navy and oceanographic scientists to explore the depths of the ocean for both military and scientific purposes. Ballard's expedition to find the Titanic was one example of this joint military-civilian partnership. The Woods Hole oceanographer and his team had pioneered a new method to finding deep-sea wrecks and the Navy financed the expedition with the proviso that Ballard's team locate two sunken nuclear submarines first. The location of the Titanic in 1985 used what was the state of the art technology at the time, and was simply out of reach for the 1940s.

Lay-person here, but I can provide some technology context.

Side-Scan Sonar is what was used to find RMS Titanic, and is the only effective imaging system for the sea floor. It was developed sometime in the early 1950s and I wouldn't expect it to be part of a military sonar system, since sub sonar is used primarily as an offensive/defensive and object avoidance tool it doesn't have much interest in the sea floor far below it.

Secondly, submarines in WWII didn't go very deep. This link provides several numbers, and though I can't speak to the veracity of the information it matches what I've seen elsewhere - much less than 1000ft. Conversely, Titanic rests over 2 miles down - over 12,000 ft.

So, considering shipping lanes and travel routes it's probable submarines passed above her resting place but they could neither see nor get anywhere close to contacting the wreck of the doomed ocean liner.

You are likely over-estimating the capability of a WW2 submarine. A U-Boat is probably better considered to be a small surface ship which is capable of submerging itself as needed, than it is a modern submarine. The crush depth of a U-Boat would be under 1,000 feet. Water is very heavy, and the boat needs to have the strength to keep it out.

By way of comparison, a modern sub would have a crush depth somewhere around 2,500ft.

Now, Titanic is over two miles down. 12,500 feet. So if a sub (or surface ship) sat above it for two weeks, they probably (Almost certainly) wouldn't notice.

The other issue is that subs generally find their way about by the sounds their targets make. Cavitation, engine noises, and the like. Titanic, being a wreck, doesn't make any noise at all. As a result, it took quite a while (About four years of on and off expeditions) of deliberate searching with active sonar and magnetic anomaly detectors with equipment four decades more modern in order to find it.