I remember this game having a stats and quest inventory screen.... But it does not seem to now.
I have the Hammer source port and the game runs and plays great, but there is no menu stat screen at all... ive looked through the options and keybindings and there is not even a setting for it.
Under the Help option in the main menu it mentions the quest item screen, and says use tab.... I get nothing.

What am I missing here?

Hmm... That's odd. I definitely see it pop up from the bottom when I press "tab". (Noting here that I'm also using Hammer of Thyrion.)

Could something be intercepting your tab-key? Or have you rebound something to "tab", perhaps...?

As to the key-bindings, the key-binding entry for this feature should be present if you go to the options screen, select "Customise controls", and scroll down to the relevant entry; specifically, it's included under the name "Full inventory", I believe. Is it not there?

The Full Inventory Thaumaturge mentioned should be the correct one to change in game.
Otherwise, the bind is also located in the data1 folder inside the Hexen II folder in Config.cfg.
Should be a line as follows (it seems to be the very first line in my fresh installed Hexen II):

bind "TAB" "+showinfo"

Note: you have to hold down TAB for it to show and stay showing. Releasing tab and the info hides again.
But, you can rebind it to something else by changing that line. removing the + may change this behavior. Never tested it.

Thanks for the info guys, I opened the config file and the bind line for showinfo was not there. Added it and it works properly now.

One other question if you know, is there a way to turn your rings off and on, such as Ring of Regeneration or Ring of Holy Power?

There is no way to toggle rings. Some auto activate under certain conditions, the others once activated keep going until used up.

default seems to be i

bind "f" "impulse 100"
bind "i" "+showinfo"
bind "o" "+infoplaque"