default or selected kernelversion does not have config value CONFIG_ATH9K_DEBUG.
Result is shown for kernelversion 5.3.17

Atheros ath9k debugging

configname: CONFIG_ATH9K_DEBUG

Linux Kernel Configuration
└─> Device Drivers
└─> Network device support
└─> Wireless LAN
└─> Atheros Wireless Cards
└─> Atheros ath9k debugging

Say Y, if you need ath9k to display debug messages.
Pass the debug mask as a module parameter:

modprobe ath9k debug=0x00000200

Look in ath9k/debug.h for possible debug masks