scoreboard players tag @p add Holding {SelectedItem:{id:minecraft:paper,tag:{display:{Name:Skip}}}}
This is supposed to add a tag to all players that are holding a piece of paper with the display name of "Skip"
Could anyone tell me why it's not working?
You need to put quotation marks around
minecraft:papersince it contains a colon, but this is not a help forum but a bug tracker. Next time post this for example in /r/MinecraftCommands.