In the feed line, between the transmitter and antenna✓Correct answer
At the power supply output
In parallel with the push-to-talk line and the antenna
In the power supply cable, as close as possible to the radio
Explanation
An RF power meter measures the power flowing along the transmission line, so it must be inserted in the feed line between the transmitter and the antenna. Placing it at the power supply would measure DC input instead, which is a different quantity.