From my rules reading (mainly from the original GDW Traveller), there is no way to either track or intercept a ship during jump. Though I don't recall any canon explanation of this, I always envisioned it as the ship being enclosed in a self-contained "bubble" of space-time created by the jump drive -- which would preclude any other ship in jump space (even if jumping simultaneously from the same starting point to the same destination) from detecting the jumping ship.
The actual practice of piracy depends on two things: the ability to intercept the ship, which in turn depends primarily on having superior acceleration and adequate delta-V (if you're using a system that tracks the latter; original Traveller didn't), and the ability to force docking, which generally would require disabling all maneuver systems (even if you can match velocity perfectly, you'd need extremely superior maneuvering to dock with a ship being intentionally tumbled, for instance). Note that destroying a ship in flight is much easier than boarding, because of the ease of preventing docking even with only attitude control; the whole point of piracy is to take value from the victim (whether in the form of salable goods and provisions such as life support consumables and fuel/reaction mass, or valuable information/personnel, or the ship itself, all of which would be lost by simple destruction of the ship).
Just as Blackbeard boarded and risked crew on ships he could have easily sunk from a standoff position, a space pirate must either board or force a landing/docking somewhere to loot the victim -- and the virtual end of large-scale piracy came when steam power required the pirates to steal compatible fuel, not just cargo (it's returned with the very high compatibility of modern fuel and very large cargo/ship values coupled with small crews and little on board protection).
The likely "best practice" for a pirate is to maintain a stationary orbit above a surface space port (or offset in the common direction of launch, if planetary rotation assist is used, as it ought to be). This will be well inside the 100D jump limit for any terrestrial planet, and gives a strong "high ground" advantage for maneuver, as when delta-V is tracked, there are a limited and predictable sheaf of economical launch trajectories even to the generic "jump distance". Second best is to be actually in port, with traffic control bribed to slot the pirates in behind a ship they choose to target, and have a ship with enhanced drives (higher acceleration) and delta-V capability. Wait for the target to launch, and then give chase from the ground up. This is more costly operation, however, and makes piracy less profitable and riskier.
Both of these methods target only outgoing ships, but that's as it should be: you won't get word of an incoming ship ahead of the ship, unless something about a ship with a low jump number and long journey is important enough to have word about it forwarded by faster ships or X-boat.