There has to be a client on the network as well. Someone has to be associated with the AP to get the Handshake. Try to log on using your phone or own computer and you'll see the handshake appear as long as your allready scanning with airodump-ng if not associate a client and then start airodump-ng then do your deauth attack using the command
Make sure your capturing all the packets first before your deauth attempt with airodump
11 = what ever channel the AP is on and capture = what ever you want to name your capture file, could be anything you want..
airodump-ng --bssid B:S:S:I:D -c 11 -w capture mon0
aireplay-ng -0 1 -a B:S:S:I:D -c C:L:I:E:N:T:M:A:C mon0
then you should see the handshake appear in the top right of airodump-ng
Hope this helps