I can't get the Layers dialog box to open.
I know there is one, as I recall seeing it many times before.
It's CMD Shift-L and it's available up in the Layers menu (bottom choice).

Some helpful back-gound, perhaps ?
I was using Inscape 48.5 and realized the problem there 1st, with an old project of mine, which I know has 4-5 layers.
Now, I recently upgraded to Yosemite 10.10.2 and located the new Inkscape 0.91 version and it seems fine But, No Layers box, again!
I even tried it with a new document and was able to make 3 layers with some content in each layer, hid them, unhid them.. all is good
but, again, no layer dialog box.

Any help is appreciated......

Well, here I am, perhaps 40 minutes later and with some further experimenting I have found a temporary, if not, final solution to my problem.
Sorry, to take up anyone’s time unnecessarily, but thought I would at least share what I found out.

Firstly, it is NOT a Inkscape problem at all.

It’s related to OSX, and the way it deals with dual monitors and/or a thing they call “Spaces”.
I didn’t mention that I use a 2nd monitor, probably due to the fact that I had been just running Inscape on my main monitor, which BTW is an iMac, so the main monitor IS the iMac.

Anyway, I went into System Prefs / Mission Control / and UN-Checked the option that says “Displays have separate spaces”, and (as it says) requires a Log Out and back in to work… which I did…

Sure enough… as it was a sort of guess on my part… that did the trick!
Actually, the document prefs. window in Inkscape was missing too.

So,… There was Inkscape working quite normal again.

I can’t say that I completely understand how this OSX “Spaces” thing works yet, but I plan to leave this setting alone, unless it affects something else here on this new Yosemite version (10.10.2).

Thanks for lending an ear, and perhaps it may even be a help to someone.
Angus

I appreciate your posting! I try to share Inkscape tips with users on Mac/Win/Nix, but I'm currently Mac-free.

Tracked here for Inkscape:

• Bug #1244397 “XQuartz on OS X 10.9 and later: limited support for multi-monitor setups”
  (XQuartz conflicts with Apple's changes of how screens and spaces interact on Mavericks and later versions of OS X)

No problem, thank You!

GAngus - thanks so much! I was pulling what little hair I had left out, trying to get a dialog box to appear doing "Bit Trace" and until I used you fix could not figure it out. Same issue - iMac, two monitors, Yosemite 10.10.2. The spaces fix totally allowed my dialog box to re-appear! You rock!