sudo cat /etc/netctl/wlp3s0-wlas (though it's the hashed key only, except if you'd used wifi-menu without -o to generate the file)
depends on the type of linux :)
EDIT: if it has to be the current network, something like this horrible bash oneliner: sudo vim /etc/netctl/$(ifconfig | grep UP | grep RUNNING | grep BROADCAST | cut -d: -f1)-$(iwconfig 2>/dev/null | grep ESSID | cut -d: -f2 | sed -e 's/"//g')
depends on the type of linux :)
EDIT: if it has to be the current network, something like this horrible bash oneliner: sudo vim /etc/netctl/$(ifconfig | grep UP | grep RUNNING | grep BROADCAST | cut -d: -f1)-$(iwconfig 2>/dev/null | grep ESSID | cut -d: -f2 | sed -e 's/"//g')