I don't know that unit so I'm making an educated guess, but those look like controls for two shelves,
or a two band shelf.
Hi-F would be high shelf frequency - the point above which everything is turned up or down.
Hi-G would be high shelf gain - how much it's turned up or down.
Lo-F would be low shelf frequency - the point below which everything is turned up or down.
Lo-G would be low shelf gain - how much it's turned up or down.
If I'm correct then my picture, as an example, would equate to approximately
Hi-F : 1k
Hi-G : 5dB
Lo-F : 200
Lo-G : -45dB
I'm heavily rounding but you get the idea, I'm sure.