$ nmcli conn edit <ID>
===| nmcli interactive connection editor |===
Editing existing '802-11-wireless' connection: '<ID>'
Type 'help' or '?' for available commands.
Type 'print' to show all the connection properties.
Type 'describe [<setting>.<prop>]' for detailed property description.
You may edit the following settings: connection, 802-11-wireless (wifi),
802-11-wireless-security (wifi-sec), 802-1x, ethtool, match, ipv4, ipv6, tc,
proxy
nmcli> describe wifi.band
=== [band] ===
[NM property description]
802.11 frequency band of the network. One of "a" for 5GHz 802.11a or "bg" for
2.4GHz 802.11. This will lock associations to the Wi-Fi network to the
specific band, i.e. if "a" is specified, the device will not associate with the
same network in the 2.4GHz band even if the network's settings are compatible.
This setting depends on specific driver capability and may not work with all
drivers.
(I only just figured out nmcli has the ability to describe things in this way.)