Wherever is the approved MLA, AP and APA style. I suspect the same holds true for whenever and whatever.
I did a quick Google poll on these:
wherever: 57,800,000 hits
where ever: 4,020,000 hits
Just for fun, I threw in “whereever” and got 78,000 hits. Not close to 57,800,000 but still a significant number. And among the prominent results were references to song titles by Metallica and Shakira and, um, “Brayan” Adams. I don’t like to cast aspersions on the spelling ability of Shakira and Metallica fans but… they say Google doesn’t lie.
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