Can someone please tell me how to check if a wlan card supports promiscuous mode
RFMON support depends on the chipset used in the adapter. Research the wlan card, find out what chipset it uses, and then find out if the chipset can operate in RFMON mode with the right driver.
This website is an excellent resource for just that.
To check if your wireless card supports monitor mode, you can use
Run in a terminal:
Supported interface modes: * IBSS * managed * AP * AP/VLAN * monitor
Supported interface modes, if you find
monitor to be present then that means that your wireless card supports monitor mode.