Hey there I'm gonna show you how to enable monitor mode in Kali Linux 2.

The traditional way for monitor mode is this. ( in my case wlan0 your might be different )

airmon-ng start wlan0

Interface	Chipset		Driver

wlan0		Realtek RTL8187L	rtl8187 - [phy0]
				(monitor mode enabled on mon0)
but in Kali Linux 2 I get an error like this.

ARP linktype is set to 1 (Ethernet) - expected ARPHRD_IEEE80211,
ARPHRD_IEEE80211_FULL or ARPHRD_IEEE80211_PRISM instead. Make
sure RFMON is enabled: run 'airmon-ng start wlan0 <#>'
Sysfs injection support was not found either;
To enable monitor mode in Kali Linux 2 you have to do the following steps:

ifconfig wlan0 down

iwconfig wlan0 mode monitor

ifconfig wlan0 up
Now the card is in monitor mode. Type the following to see some Access Points around you

airodump-ng wlan0

try to inject with aireply-ng to see if the injection works

aireply-ng -9 wlan0
if the injection is not working you have to install the compat-wireless driver for you card.