Два способа:

# Первый
#
alexander@alexander-ThinkPad-X201 ~ $ iwconfig wlan0 | grep Qual
          Link Quality=66/70  Signal level=-44 dBm  


#Второй
#
alexander@alexander-ThinkPad-X201 ~ $ iwlist scan 
eth0      Interface doesn't support scanning.

lo        Interface doesn't support scanning.

wlan0     Scan completed :
          Cell 01 - Address: E0:3F:49:8A:51:68
                    Channel:6
                    Frequency:2.437 GHz (Channel 6)
                    Quality=66/70  Signal level=-44 dBm  
                    Encryption key:on
                    ESSID:"bbb"
                    Bit Rates:1 Mb/s; 2 Mb/s; 5.5 Mb/s; 11 Mb/s; 18 Mb/s
                              24 Mb/s; 36 Mb/s; 54 Mb/s
                    Bit Rates:6 Mb/s; 9 Mb/s; 12 Mb/s; 48 Mb/s
                    Mode:Master
                    Extra:tsf=00000000224a4f10
                    Extra: Last beacon: 76672ms ago
                    IE: Unknown: 0003626262
                    IE: Unknown: 010882848B962430486C
                    IE: Unknown: 030106
                    IE: Unknown: 2A0104
                    IE: Unknown: 2F0104
                    IE: IEEE 802.11i/WPA2 Version 1
                        Group Cipher : CCMP
                        Pairwise Ciphers (1) : CCMP
                        Authentication Suites (1) : PSK
                    IE: Unknown: 32040C121860
                    IE: Unknown: 2D1A7C191BFF00000000000000000000000000000000000000000000
                    IE: Unknown: 3D1606081100000000000000000000000000000000000000
                    IE: Unknown: DD090010180202102C0000
                    IE: Unknown: DD180050F2020101800003A4000027A4000042435E0062322F00