For QoS over WiFi you should enable WMM (presuming the clients also support WMM).
If you are sending the voice-traffic through the controller (tunnel-mode), the Voice/SIP ALG in the controller should detect ingoing VoIP calls. With this CLI-command you check calls being made through the controller:
show voice call-cdrs detail
The field DSCP should show the correct IP DSCP value (46 or 56). The field WMM should show a value of 6 or 7.
You can also create a packet-capture on the controller for a specific WiFi client which should capture 802.11 data-frames and IP-frames. You can check those headers if the correct QoS values are set.
packet-capture destination local-filesystem
packet-capture datapath wifi-client 00:11:22:33:44:55
Then perform a "copy logs" to extract the PCAP.