DECLARE @data NVARCHAR(MAX)
SET @data = 'INSERT INTO #coco  ' + '([' + @val + '])' + ' SELECT [USER_ID] FROM [dbo].[Sheet1$] WHERE [Standard_Name] LIKE ' + @val

EXEC sp_executesql @data

DECLARE @data;
SET @data = N'INSERT INTO #Coco (' QUOTENAME(@val) + N')' + NCHAR(10) +
            N'SELECT [USER_ID]' + NCHAR(10) +
            N'FROM dbo.[Sheet1$]' + NCHAR(10) +
            N'WHERE [Standard_Name] = @val;'; --As this doesn't contain a %, there's no need for LIKE
EXEC sp_executesql @data,
                   N'@val = sysname', --guessed datatype
                   @val = @val;