I saw this interesting question--what is the speed of dark-if it even has a speed?

Dark is the absence of light.  Dark would only take over when the light source is blocked, turned off, or otherwise stops emitting light.  Dark would take over at the speed light as the photons of light continued moving.

Of course in the strict sense, 'dark' does not have a speed.

There is a thing called dark energy but as far as i know it has nothing to do with speed.

Isn't 'dark energy' an un-observed correction factor to explain the speed of objects in space?  In other words it is only theoritical at this point?

Yes it's still theoretical more hypothesis stage i believe, explanation for what they are observing and for a lack of a better way of explaining it properly just call it that. There is an unseen force operating which that they tell but can't fully understand what it's significants is

Speed of dark has to be faster than the speed of light. Think about a black hole, it is dark and nothing even light can't escape a black hole.

This is gravity or gravitons.