The problem with titanium for knives is that there are a lot of alloys out there. Some hold an edge better than others. Some are just plain pains in the butt to get an edge on, and others won't hold it.
I started cutting meat at the age of 8 in my family's grocery store and learned to sharpen knives at the same time. Over the last 50 years I can say that nothing comes close to a good carbon steel blade for edge retention and ease of sharpening. That said, they aren't great for diving unless you religiously care for them.
So we have alternates. Stainless, titanium, and ceramics.
Out of those my preference would be for stainless, followed by a good ceramic, and titanium at the bottom.
After you get a functional edge on a blade, you have to decide what you want to do with it.
For some stuff you don't need a razor edge that tends to get nicked or rolled easily.
I've always preferred a single bevel on the knives I have that get most of the use. It's strong, easier to maintain, and it's what traditional katanas are set up with.
Double bevels have the disadvantage of introducing more errors in sharpening.
I have on titanium blade that is very good at holding an edge and taking one.
War Galley XII Titanium Marine — USGladius
This one is also balanced and throws nice. But it's 380 bucks and they only made 600 of them. I got mine at a Beneath the Sea Show at price I could not pass up because he wanted to sell out and not take any back with him.
The rest of my knives (save 3) are all carbon steel of some type and the 3 are dive knives. One of which I carry on a regular basis. The others are ones I've picked up as part of a lot of gear because they are pretty much useless. The one that's not is a Dalton Safety knife that Deep Sea Supply sold. It's basically a wood handle steak knife with the tip broke off.
As for sharpening any blade a good stone is a must. A 3 way multi-stone is what we always used in the butcher shops and one that I liked the most had medium, fine, and extra fine stones.
Coarse stones are more for setting up an edge. Once you have one, it should not need to see a coarse stone again unless it gets badly nicked.
For my katana, wakizashi, sgian dubh, and custom Scottish dirk I also have 600 and 1000 grit Japanese dressing stones.
Always sharpen with some kind of lubrication. Water works best overall.
When sharpening I always get the best edges with a combination of pulling and pushing but that's with nearly 50 years of experience holding the right angle and applying the right pressure.
On my kitchen knives I also keep a good steel handing for dealing with edges.
While titanium is good for corrosion and rust resistance, unless you paid a couple hundred bucks for that knife, the Ti alloy used is likely the cheapest they could find and use of the Ti is more a marketing gimmick than for actual function.
You could also look for a pro sharpening service and have them put an edge on it. Then treat it with care.
For underwater stuff a pair of shears or line cutter is usually much more functional and likely to be used. Knives are cute. But not as much use as those two items.