I am a newbie who has just (re-)begun using Blender, version 2.8, on a retina Macbook Pro from around 2014 with MacOS 10.14.2 ("Mojave"). GPU is (selectable) an internal discrete NVIDIA GeForce GT 750M (2048 MB) and an on-board Intel Iris Pro (1536 MB). Neither of these are recognised by Blender when I try to select them.
So I visited the NVIDIA site, hoping for a CUDA driver update, but no suitable "Latest drivers" are listed there for MacOS, only for other operating systems (Windows, Linux, Solaris).
As far as I can tell, this situation is the result of a debacle between Apple and NVIDIA, where Apple is (currently?) not authorising NVIDIA drivers under MacOS Mojave.
Especially annoying, since I had specifically selected a Macbook model that came with a NVIDIA GPU, with use of Blender in mind. At the time I bought it (2016), AFAIR, Blender had either more or only support for NVIDIA CUDA.
I can only hope that this apparent inter-company situation will eventually be resolved.
Currently my Macbook has NVIDIA CUDA Driver version "410.130", GPU Driver version "318.104.22.168.10.103". Latest in the NVIDIA drivers archive for "All Mac products" is "418.105". I hope to install (and use) that one, as an unapproved download, if Mojave will let me. Following a system backup (via Time Machine) that is...
Any constructive advice / workarounds welcome.