Someone gave me a titanium dive knife, but the thing is

1. How do I sharpen it
2. How long does it stay sharp
3. Do I just use normal sharpening stone?
4. Can I take it to a hardware store to have it sharpen for me
5. Does sharpening a titanium knife grinds down the blade
I have no clue on what and how to sharpen it!
Please try to answer all 5 thanks
1. You sharpen it like any other knife. Personally, my favorite edge is put on with a loose, worn belt on my belt grinder. Followed by a good stroping, this results in an edge that will not only shave, but will cause the hair to leap off in terror. And the slightly convex shape of the bevel adds material behind the edge, making it stronger than the more common flat or concave bevels. The downside is that unless you're really really good, you will not be able to touch up the edge in the field.
2. How long it stays sharp depends on how fine an edge you give it, how much you use it, and how you use it. The finer the edge, the faster it will dull. The harder the use, the faster it will dull. Bear in mind that, barring abuse that chips the blade, knives don't really ever need to be sharpened more than once. As they are used, they only SEEM to dull. What really happens is that the super thin burr at the edge folds, and needs to be straightened. You do this with a steel (SMOOTH!!!) or ceramic(better) rod. And it also helps if you strop the blade. I use an old razor strop or (better yet, but dangerous for beginners) a buffing wheel. Titanium, while totally rust proof, is softer than steel, and thus needs to be touched up more often. I have a small ceramic rod I carry in my bag for this purpose.
3. Yes. If I'm not putting on a convex edge, I use a good flat diamond stone. Start with a coarse stone and work progressively finer till you reach the edge that you desire. If you want to use the blade for slicing (most likely, on a dive knife) work across the blade from edge towards the spine, as if you were shaving the stone. This will put micro-serrations on the blade and helps with slicing. On non-dive knives, if you want a shaving edge, work along the blade lengthwise, progressing to super-fine stones and eventually stroping the blade to polish the edge.
4. I would not let a hardware store touch any blade other than a lawn mower. You are extremely unlikely to find someone there who can put on a proper edge using power tools without destroying the temper of the blade.
5. Sharpening any blade involves removing metal to shape the bevel to the shape and angle chosen. Touching up the edge, as mentioned above, does not, if you're doing it properly with a smooth steel or ceramic rod.