For implementing an 8 direction animation in Unity, the recommended component to use is SkeletonAnimation.

The SkeletonAnimation component provides a larger set of functionality and more ways of customization compared to SkeletonMecanim. It is also the preferred method for using Spine skeletons in Unity due to its higher customizability and fewer limitations. Using SkeletonAnimation will allow you to better manage and optimize your animations, especially when dealing with complex setups like 8 direction animations.

For more information, you can refer to the spine-unity Main Components documentation.

thcha If your skeleton is relatively simple, you can set up a single skeleton which can face 5 directions, with the remaining 3 directions obtained by setting the Skeleton's scaleX to -1. You can then simply make sure that the appropriate animations play as you manipulate them in the game. You can see an example of a simple skeleton facing 8 directions here: https://esotericsoftware.com/spine-twitch#video-FPaqO0Xlh4w

However, in the case of complex skeletons, it can be difficult to manage 8 directions in one skeleton. While covering all directions with a single skeleton has the advantage of making it easy to reuse the same animation, it also means that changes made in one direction may affect poses in other directions, and before you know it, poses in other directions may be broken. Therefore, for skeletons that are more complex than the one linked above, and that require complex animations such as attack and special skill moves, it may be easier to manage them by splitting them into two skeletons, one for the front and one for the back, or even three skeletons, for example by creating a separate skeleton for the side view.
If you were to do this, you would have two or three SkeletonGameObjects under one GameObject (say, a GameObject named Player) and switch the skeleton to be displayed according to the direction the Player is facing.

You may find the following thread helpful:
https://zh.esotericsoftware.com/forum/d/12335-animating-isometric-character-recommendations