A transport unit will have Icon on it if its loaded. You can see what its carrying.
Click on the hex the unit is in, then click on unit presence (far left middle button IIRC), then hover your mouse over the transport unit. A popup will show what it has loaded up and the transport order. IE...Idle or Destination so and so.
Can I load planes onto transports if so how? they seem to fly over and go back to the previous place they can from. I wish to move some planes across the pacific and there range will not allow them to fly over so I was attempting to transport them.