I just bought a new (second-hand) bike (Orbea Asphalt sport) and I was looking at the tire and found out it was a tubular tire, a Continental Grand Prix, but on the sides you can read 'only mount on a hooked rim'. Is it possible for a tubular tire to be mounted on a hooked rim?
Tufo makes tubular clinchers. Clement made something similar in the eighties, called the Ritmo, I believe. I don't think Continental does, I'm pretty sure they're just regular clincher tires.
You can ride tubular tires on clincher rims in an emergency, but they'll roll off the wheel if you're not very careful in the corners.
I think you are confused between tubular and tubeless. Tubular tires are "all in one" tire where the inner tube is sewed inside the tire. Tubeless tires look like regular clincher tire and hooks in specially designed rims; these tubeless tire and rim provide an airtight seal so they can be inflated without an inner tube. Regular clincher tires are very similar, but require an inner tube to contain the air.
So a tubeless tire does require a hooked rim, but they are not tubular tires.
Additional detail : clincher tires can be installed in tubeless rims with no problems.
It's not a tubular tire. Tubular tires are held to the rim with glue and are pretty much only used in racing due to their cost and the hassles of replacing them when they flat.
Clinchers (including tubeless clinchers) rely on a wire or Kevlar bead in the tire and a sidewall on the rim to hold the tire to the wheel. Some rims have a lip - or hook - on them to help hold the tire on the wheel, especially in the event of a flat. Using a tire intended for use on a hooked rim on a rim rim that does not include a hook/lip could result in the tire peeling off in the event of a flat. If this happens at high speed the results could be disastrous.