To be able to sniff the probe requests, your Wi-Fi network interface must be set to monitor mode.
sudo ifconfig <wireless interface> down
sudo iwconfig <wireless interface> mode monitor
sudo ifconfig <wireless interface> up
For example:
sudo ifconfig wlan0 down
sudo iwconfig wlan0 mode monitor
sudo ifconfig wlan0 up
To kill all the interfering processes:
sudo airmon-ng check kill
To enable the monitor mode:
sudo airmon-ng start <wireless interface>
For example:
sudo airmon-ng start wlan0
sudo probequest -i wlan0
Here is a sample output: