MILITANCY, COLONIALISM, the “subjunctivity” that Samuel R. Delany identified as key to science fiction, the possibilities of the essay-film: Certain concerns and themes may be traced across the career of the Otolith Group. But Otolith, founded in 2002 by Anjalika Sagar and Kodwo Eshun, has defied attempts to neatly summarize its practice. On the occasion of “Xenogenesis,” a traveling exhibition opening July 7 at the Irish Museum of Modern Art, Dublin, after stints at the Van Abbemuseum in Eindhoven, the Netherlands, and the Sharjah Art Foundation, critic Ed Halter and writer Tobi Haslett survey