Getting speed difference between signal comparison using Dynamic Time Warping
There is no single "speed difference".  The way DTW works is that it checks whether you can find a match by slowing up and/or speeding up one of the signals.

For instance, suppose you want to match signal X to signal Y, which last 3 minutes.  It's possible that the best match might involve speeding up signal Y for the first minute, slowing it down for the second minute, and leaving its speed unchanged for the third minute.  Thus, there's no one speed, no one speed difference, and no simple answer to whether Y is faster than X or not.  Rather, the answer is: "faster in parts, slower in others".

Once you find the best match using DTW, you can easily recover in which parts Y was faster than X, and in which parts Y was slower than X.  I encourage you to do a bit more reading about how DTW works -- it'll probably all become clear as you understand the gist of the idea.