grep + bash

iw dev wlan0 station dump | awk '{print $2}'

:~# iw dev wlan0 station dump | awk '{print $2}'
74:e5:0b:cd:f9:e4
time:
bytes:
packets:
bytes:
packets:
retries:
failed:
-70
avg:
bitrate:
bitrate:
throughput:
yes
yes
short
yes
no
peer:
48:50:73:f5:c2:2c
time:
bytes:
packets:
bytes:
packets:
retries:
failed:
-82
avg:
bitrate:
bitrate:
throughput:
yes
yes
short
yes
no
peer:

iw dev wlan0 station dump | awk '/Station/{print $2}'

clients=$(iw dev wlan0 station dump | awk '/Station/{print $2}')

for client in $clients; do
    ...
done