From the author's README on Thunderstore

Ghost Classic mask from MW 2019, comes with the glasses and a separate mask version to fit hats

If you wish to wear this with hats, you need the mod "Wardrobe Tabs and Layers" by Fourth_Studio. This makes it so that you can put the mask into its own custom tab, then you can wear it with hats

Masks are in hat section named as:

Ghost Classic Mask
Ghost Classic Mask for hats

Glasses are in eyewear section named as:

Ghost Glasses

Install Ghost Classic Mask

You need ReSkate and your own copy of skate. on Steam.

Open ReSkateLauncher.exe and go to MODS.
Search for Ghost Classic Mask and click install. The launcher also installs anything it depends on.
Press PLAY. In game, the MODS tab of the ReSkate menu (Insert) turns it on and off.

Or install it by hand: download the .zip and drop it on the launcher window, or unzip it into its own folder in Mods\ beside Skate.exe.

Maps show up in the ReSkate menu's level list. To join a server running a custom map, you need the same map installed. If the game won't load after installing, see known issues.

skatemods doesn't host or review this mod. The download comes straight from Thunderstore. Only install mods you trust, because scripts can run code.