Hi gizmo,
look at this video:
At 1:47 JTAC sends the target location via datalink to the player aircraft. At this step, you will have to make the TAD SOI and hit TMS left short. This will clear the "NEW TASKING" message. Then you need to push the OSB labeled "WILCO". This acknowledges that you have received the target data.
Now, you will see that a red symbol has appeared on the TAD. You can see it in the video at 2:24 right next to the yellow waypoint symbol.
This symbol marks the target location. You need to move your cursor on the TAD over this symbol and hit TMS up short to hook it up.
Now, with the TAD still being your SOI, hit TMS up long to make the TAD your SPI.
Now, to see your target in TGP, make the TGP your SOI and push CHINA HAT forward long to slave your sensors to your SPI.
Now, in the Devils cross missions your target is a moving tank column, so it will most likely have moved away a bit from the location the JTAC gave you so you have to look around a bit with your TGP to find your target. Try searching along the road(s) as the tank column will not move off-road. There are several columns of tanks, IFVs and artillery, which are close to each other so if you have found one column "your" column is most likely not far away.
Hope that helps!