As much as I enjoy TUC, it doesn't do a good job of establishing where Praxis is relative to Kronos. We know that it's close enough that it has serious environmental implications. However, that would imply that the borders of the Klingon Empire are such that Kronos and Praxis really straddle the edge, because that's really the only way the Excelsior could be close enough to get hit with the shockwave without crossing into Klingon space.
I guess that's for another topic, though.
It was a sub-space shockwave, so really it could be anywhere.
I guess, not that it really helps though. It just makes it even more implausible that the Excelsior would be in the exact path of a shockwave that couldn't have been more than a few miles high which originated from lightyears away. All the better is the fact that it snuck right up on them. It'd be like driving a car into a tree... in Antarctica.