Corrected entry: The Excelsior detects the incoming shockwave from the exploded Klingon moon Praxis and is hit seconds later. Assuming that the Excelsior in these times isn't operating within Klingon borders (or even the Klingon solar system) and is monitoring the neutral zone light years away, the Excelsior cannot be hit or even be surprised by a shockwave coming from so far away. Gravitational shockwaves or explosions (even huge ones) are not faster than light. It would take years to reach the Excelsior.
Goekhan
12th Oct 2019
Correction: It's described as a "subspace shockwave" so by Star Trek parlance this is some type of disturbance that can indeed travel faster than light.
TonyPH