Quotename() function is used to return a unicode string with delimiters. A delimiter can be a single quote, double quote or braces ( or [.

select 
	quotename('test','''')  as single_quote,
	quotename('test','"') as double_quote,
	quotename('test','(') as brace,
	quotename('test','[') as sqaure_beace

The result is

single_quote double_quote brace    sqaure_beace
------------ ------------ -------- ------------
'test'       "test"       (test)   [test]

Consider the following example. A variable @display is used for a display purpose ie to show them as part of the resultset.

create table #t(data varchar(100))

insert into #t(data)
select 'test' union all
select 'testing' union all
select 'nothing' 

declare @sql varchar(1000), @display varchar(100), @data varchar(100)
select @display ='Reporting', @data='test'

select @display as display,data from #t where data=@data

The result is

display        data
------------   ------------
Reporting      test

What if a single should be appended to the value Reporting?. We can use this method

select ''''+@display+'''' as display,data from #t where data=@data 

The quotename can be used in this case

select quotename(@display,'''') as display,data from #t where data=@data 

But beware that the Quotename() function will not work if the input's length is more than 128 characters