I have the LEGO 60139 set for my child. If I buy LEGO 8293, will I be able to motorize the truck in 60139 set?
You are not likely going to be able to add the power functions motor to this set without some major modifications. The truck in the set uses pin type wheel connections, the motors normally use technic axle style wheels, and there isn't really any extra room internally to place the motor.
1You might be able to contain the battery box in the trailer but it will be very difficult to include the motor in the truck (as you said) without major modifications although the biggest issue would probably be implementing steering for a City scale vehicle.– Ambo100 ♦Dec 8, 2017 at 0:30
1Also relevant: How can I motorize City-scale wheels?– Ambo100 ♦Dec 8, 2017 at 0:32