I have an iMac with a Spanish ISO keyboard (I live in Spain) and I am using layers and adjustment layers. On my keyboard there is no / (backslash) key only Alt \ combination. So in Photoshop how do I toggle layer mask on/offf?
Looks like on that keyboard the / is Shift + 7 for the / .. does that work for you?
The other options are to hold the shift key, and left-click on the Layer Mask thumbnail to toggle the Layer Mask effect. Or you can right-click on the Layer Mask thumbnail, and choose Disable / Enable for the Layer Mask.
On further research, you should be able to adjust this keyboard shortcut to one that is easier on your keyboard using Edit > Keyboard Shortcuts > Tools > Toggle Preserve Transparency. See this screenshot.