Interesting how much talk this premise has generated about Germany and offensives against British India, but speaking about the Scramble for Africa, and a conflict rooted in the Fashoda War, I would expect a conflict centered in Africa.
A Fashoda war would start over South Sudan and its central antagonists would be Britain and France, with the other powers as bit players or sitting on the sidelines.
An escalated war would radiate out from Eastern Africa. The immediate prize for the victor would be the Eastern Africa region, with colonies like Sudan, Chad, Equatorial Africa, Djibouti, Somaliland, Uganda, and Kenya at stake.
A decisive win in an escalated war would see much of pink British Africa turned French purple, or French purple Africa turned British pink. I suspect, given British clear naval superiority, than English pink will predominate over much, much more of Africa, so there will be a big purple to pink shift.
If Britain makes a total clean sweep of the oceans and seas against the French, Britain can wipe all the purple off of Africa.
But that would be quite dramatic, and the French probably could be competitive in the Mediterranean, and have pockets of substantial military strength, especially in North Africa, like Algeria, and West Africa like Senegal, so perhaps, the Mediterranean coast of Africa from Algeria or Morocco to Egypt could end up French dominant, with Sub-Saharan British dominant. Or the split could work out some other way.
The other place where large British and French colonial territories meet is the border of Indochina and Burma in Southeast Asia. Clearly, Britain can raise far more troops from India than France can from Indochina.
As others have mentioned, France's ally, Russia, can theoretically threaten British India, but logistics and terrain mean they can't project large numbers very far very fast. The Russians I imagine could leverage British preoccupation to gain a good upper hand in Persia though.