Minecraft 1.12.2 How to /clear item that have a specific enchant and name

I’m expanding your command and pointing out all the errors in it:

/clear @p minecraft:paper 0 1
{ 
    tag:{  # “tag” should not be used in /clear command
        ench:[
            {
                id:16s,
                lvl:1s
            }
        ]
    }
}, # this extra “}” closes the final tag before you get to the display section.
{
    display:{
        name:"custom name" # “Name” misspelled as “name”
    }
}

So in summary:

• Don’t use tag in the /clear command.
• Make sure you are balancing your brackets. You used one too many }s.
• The name tag is misspelled. Correct tag is Name.

Fixed command:

/clear @p minecraft:paper 0 1
{
    ench:[
        {
            id:16s,
            lvl:1s
        }
    ],
    display:{
        Name:"custom name"
    }
}