You definitely have water damage, from a leaky shower. You are very lucky if there is no mold in that wall. It looks very bad.

Looks like a leaky shower curb. Very common point of failure. Shower replacement sooner than later on the agenda.

Thanks for thr replies. I will check with my tile guy for redoing Shower. I wonder if it would involve replacing thr tub too, as it's adjoined and cabinets are attached to the tub wall. Do we need to redo everything?

I can check with my tile.guy and cabinet guy.

What can be done about the wall damage? There's a crack on the wall as shown in pic. Whom should I contact for this kind of work?

Thanks for looking into this!

You wont know some of those answers, until you get a good contractor in there, and tear apart that shower, and wall. The wall, will most likely have to be rebuilt, as the damage looks pretty bad. Make sure who you hire to do this knows the proper way to waterproof a shower, so its all done right, or you could have the same problem over again. You may have to have some plumbing redone too. Go to u tube and look at videos, for waterproofing showers, so you know a bit more about how its done properly, so you can see, that your contractor is doing it correctly.

" What can be done about the wall damage? There's a crack on the wall as shown in pic. Whom should I contact for this kind of work? "

That will all get gutted along with the entire shower. Who else you may need will depend on your tile setters abilities, skillset and how much of this type construction/repair he will do. Ask him. He will either tell you need someone else and here is who I would call or I'll handle it all for you. We have no idea with that.

The 'crack' is the edge of the drywall corner bead--where it detached from the drywall. Maybe because it was glue starved/ maybe because of the moisture/ likely both. Like MWM said, that will all get demo'd when the shower area is gutted.

I would suggest using PVC baseboard when the room gets put back together. Appears that the existing trim is MDF--I would never use MDF in a bathroom. Least bit of moisture on MDF and it swells up and disintegrates.

you need a general contractor.

There looks like there is mold around the other side as well. I would bet there is mold in that wall.

Your shower is leaking, guaranteed. This isn't going to be cheap to fix.