How do I know my Samsung S8+ Model SM-G955FD is Exynos and Snapdragon? I want to root my S8+. I found two type of TWRP recovery file Exynos and Snapdragon for my SM-G955FD.I wanted to know which one is suitable for my mobile?
The model number unambiguously determines the device's core configuration - if it says G955F(D) everywhere on the device (especially in Download Mode, which AFAIK can't be faked), then you can be sure that it's an Exynos variant.

Boot into Download Mode with the key combo VOL- + BIXBY + POWER, and you'll be greeted with a screen like below, where the model number will be shown after "PRODUCT NAME".



EDIT: For a more detailed breakdown of all S8+ models (full specs), check out this list from PhoneDB: Samsung Dream 2 ("Dream 2" is the development codename of S8+)