Does anyone know if the black mxq supports 5ghz wifi? If not, how about the mxqpro 4k.
Different manufacturers equipped their devices under the same name with different wifi chips, so your question cannot be answered.
But since we have discussed the wifi chips in both of them before (in this topic), I can answer directly.
Your MXQ (S805) has this:
Bus 001 Device 003: ID 0bda:0179 Realtek Semiconductor Corp. RTL8188ETV Wireless LAN 802.11n Network Adapter
RTL8188ETV -> The answer is that it is only capable of 2.4 GHz (802.11bgn).
Your MXQ-4K (S905) has this:
...
configuration: broadcast=yes driver=rtl8189es driverversion=3.14.29 firmware=N/A ip=192.168.1.136 link=yes multicast=yes wireless=IEEE 802.11bgn
RTL8189ES -> The situation is exactly the same, the only difference is that this chip connects to SDIO instead of the internal USB line: 2.4 GHz only (802.11bgn).
So, if you are going to install a wifi router (or AP) that only works in the 5 GHz band, it will not communicate with any of them.