Robert Farris Thompson, American's most prominent historian of African art, says that funky is derived from the Ki-Kongo lu-fuki, meaning "positive sweat" of the sort you get from dancing or having sex, but not working. One's mojo, which has to be "working" to attract a lover, is Ki-Kongo for "soul". Boogie comes from mbugi, meaning "devilishly good." And both jazz and jism likely derive from dinza, the Ki-Kongo word for "to ejaculate."
Have questions about etymology? Ask an art historian!
The fact is that the origin of all these words is unknown, except for funky, which is probably from French.
The reference is Flash of the spirit: African and Afro-American art and philosophy by Robert Farris Thompson. This is what he writes:
Many a Ki-Kongo-derived word has been described by etymologists as "origin unknown." The word "jazz" is probably creolized Ki-Kongo: it is similar in sound and original meaning to "jizz," the American vernacular for semen. And "jizz," suggestive of vitality, appears to derive from the Ki-Kongo verb dinza, "to discharge one's semen, to come." Dinza was creolized in New Orleans and elsewhere in black United States into "jizz" and "jism."
The slang term "funky" in black communities originally referred to strong body oder, and not to "funk," meaning fear or panic. The black nuance seems to derive from the Ki-Kongo lu-fuki, "bad body odor," and is perhaps reinforced by contact with fumet, "aroma of food and wine," in French Louisiana.
He goes on; you can read the whole thing.
This is pure speculation, as far as I can see, and in fairness Thompson qualifies his claims with "seems" and "probably" and "appears". It is not etymology; etymology requires evidence. As Grant Barrett says in his review of Daniel Cassidy's book How the Irish Invented Slang:
Evidence. Above all, Cassidy needs to support his claims with published evidence that shows the etymological path. Dated, continuous, in-context quotations from any written source will always be superior evidence over phonetic speculation based upon national, linguistic, or ethnic pride.
I am bothered that the authors of Sex at Dawn would simply repeat Thompson's claims, without bothering to consult an expert.