What to call expressions like "Google-Fu"

These kinds of words are commonly lumped together with all new formulations as neologisms.

Their meaning, in the case of the combinatory neologism, is fundamentally metaphorical: it asks us to understand one thing in the context of another. For example, the word "Google-Fu" asks us to consider one's ability to effectively utilize the Google Search Engine as though it were a martial art, a perhaps more easily understood physical skillset honed over years of practice with connotations of flexibility, finesse, and power.

Because of this metaphorical component, it is also possible to describe these combinatory neologisms as kennings. This is a very old concept in the English language's deep past, deriving from the poetic sensibilities of its Anglo-Saxon speakers - kenning is a metaphorical combination of two concepts for the purpose of emphasizing certain characteristics about what they describe. The stereotypical kenning trotted out from Beowulf would be to describe the sea as a "whale-road" - emphasizing the greatness and alienation of the ocean - it is a large place fit for monsters to travel through, not so much puny hominids in rickety wooden vessels. I personally like to describe Stack Exchange as a wizardry-machine.

I've never even been to this end of SE but as I'm here I'll drop in the rather more obvious and probably equally improper portmanteau and be off.

(also portmanteau word) A word blending the sounds and combining the meanings of two others, for example motel or brunch

[Oxford Online Dictionary]

A blend:

• (Linguistics) A word produced by combining parts of other words, as smog from smoke and fog.

(AHD)