There is no equivalent of the Windows "context menu of what's currently selected" key.
If Mouse Keys is turned on in Universal Access in System Preferences, Control [Numeric Pad 5] will act as a regular right-click, i.e., it'll bring up a context menu where the mouse is.
But I doubt that's what you're looking for.
If you want a shortcut for Spelling and Grammar in Word,
it's Command Option L to bring up the window
Then use Tab to go to the 2nd list and Up/Down to select the proposed correction, then OK.