Edit Animation Layer will be the option when you don't have a character selected. So for example if you have a prop selected then Edit Animation Layer will be there instead of Edit Motion Layer.
You mention using mocap so I'm assuming you are doing character animation. In this case make sure you have your character selected in Scene Manager. Then Edit Motion Layer should be selectable.
Please Note: Your character needs to be rigged with bones for Edit Motion Layer to be an option. Any standard CC characters or humanoid characters will be fine. An unrigged character is just considered a prop so you won't see Edit Motion Layer as an option.