Activate “Mouse Keys” (in System Preferences, search for “mouse keys”, turn it on). Position the mouse cursor. Hold Control. Press and release the keypad's 5 key. Release Control.
Spell Check via Keyboard
There are standard shortcuts for the built-in spell checking. Not all applications may have these menu items.
⌘; — Edit > Spelling > Check Spelling
This selects the next ‘misspelled’ word.
⌘: — Edit > Spelling > Spelling…
This selects the next ‘misspelled’ word and opens the Spelling floating window. To focus the floating window without using the mouse, you can use the “full keyboard access” shortcuts (enable them in System Preferences, search for “full keyboard access”, it (and the extra shortcuts it enables) are under the “Keyboard Navigation” subtree.
You may need to reassign the shortcuts. The default for “move focus to the floating window” is ⌃F6, but that seems to be used by the editor here on SO, so I needed to change it to test it while composing this answer (I used ⌥F6). Once focus is on the Spelling floating window, you can
dismiss it with Escape, or use Tab to move to the various controls, and with the replacement textbox focused, you can
use Up and Down to select replacements, and type a replacement, and use Return to activate the default button: Correct"