Which of the following methods is the best way to crack the network key if a WPA2 wireless network is discovered during a pen test?

A Capture the WPA2 authentication traffic and crack the key.

explanation

WPA2 is a strong encryption method, but with enough time, practically everything can be hacked. Capturing the password pairwise master key (PMK) during the handshake is the only method to achieve it, and even then it's very difficult if the password is complex.