Advice please to clear shower drain. I have used bicarbonate soda and vinegar which didn’t help. Then I bought a snake auger but when I take chrome cover off shower drain, all I cannot see any sign of the hole leading to pipe work and I’ve tried feeling for it with flexible wire. If I look under the shower I can see where drain pipe goes off the trap but no entry hole when I try from shower tray. I wondered if there was a hair trap which should lift out but plastic fitting seems to be secured into shower tray. I’ve tried turning it but no movement at all. I’d be grateful for any tips. I’d post photo but not sure how to add them. 
Plumbing – Slow draining shower
plumbingshower
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I disagree with BMitch as far as if the P-trap will come apart. (Possibly the first time we've disagreed?) The metal nut could not be where it is if the joint did not separate. The rest of his answer I agree is the easiest fix. However, if possible, physically cleaning the trap is preferable to a chemical approach. I'm assuming there is a slip fitting just out of the picture, just as there is in non-disposal side. By detaching the metal ring in the first photo and the unseen slip joint, the trap should be able to be removed.
Even without a slip joint, the pipe could be detached right at the disposal itself. This could actually be preferable as it would allow the P-trap to swivel, which may help in loosening the nut. Are you sure you are trying to turn the nut the correct direction? I'm not saying you don't know how to loosen fasteners. The direction depends on which piece the nut is threaded onto, which is not always clear in plumbing.
The curved shoulder of the nut tells me it is threaded onto the U-bend, so the nut is turned anti-clockwise when looking down at it. It's hard to tell by photos, but you appear to have decent access to the nut from the left side as it is below the pipe coming in from the other side. Even though the opposite trap may be in the way for fully turning a wrench, you seem to have enough room to place the wrench handle near the trap and pull right.
As for counter force, if pulling on the pipe itself isn't working, try a large screwdriver wedged in the inside of the U-bend. If you have the right wrench, the ring nut shouldn't offer a lot of resistance.
The next step is to snake the drain with a plumbing snake:
Or to call a plumber.
Best Answer
I've dealt with this recently with two shower/tubs. I'm going to assume that you mean a combo and just a shower because those (at least in my experience) go straight down.
For me, it was really hard to tell which way the drain went at the bottom, but it went straight back under the tub. Please don't take this to mean that yours necessarily does.
For the first one, I put a snake down and was able to get quite a bit of hair out. The snake ended up getting stuck on the way out and I deformed it some. With the second, I just put some lye down the drain. This isn't really ideal especially if you have a septic field, but is fast and easy.