Basically, this famous basque drink is composed of red wine & coke, fifty/fifty (this is the most important thing). It is supposed to be served with ice if available and you can also add a slice of lemon. Don't forget to stir it well before drinking.
See more detailed instructions to make the perfect kalimotxo (IMHO) (in Spanish).
"Calimocho" (weird) Wikipedia webpage (in Spanish) where this website is
referenced as the first one about kalimotxo.
Franck Celhay, Is the “kalimotxo” a heretic cocktail?" (see preprint), Decisions Marketing, October 2008.
Beyond the ironic title, this article analyzes the pros, cons and whys about the impact of kalimotxo in consumption habits of young people.
One page is dedicated to kalimotxo in the prestigious publication
"Spirits & Cocktails", edited by David Wondrich with Noah Rothbaum, published by Oxford University Press, 2022.