I've played about 6 hours or so over a couple days and I just can't seem to find anywhere I can click or any box that would tell me my target ships speed. I do see an indication of maximum possible speed in the targeting info on the right hand side, though ships turn, then they get hit and have one or more of the engine icons above them. So far it seems the only way I can roughly gauge their speed is by looking at the range circles vs my ship, once I've selected one of the enemy ships. If the rings are getting closer, then they are closing on me and if their course is somewhat straight and mine is too, then they must be going faster than I am. Thankfully, I can see my own ship's speed.
I know that estimating speed was an important part of the gun aiming equation, so there must be some way to tell how fast an enemy ship is traveling. I just haven't found it yet. If you know, please tell me. Thanks!