Also you cannot have spaces in element names, <Data Extract> needs to be <DataExtract>

DECLARE @SQL NVARCHAR(MAX) = '<DataExtract><Graduates><Candidate><FirstName>Shaun</FirstName><LastName>Slabber</LastName></Candidate><Candidate><FirstName>paul</FirstName><LastName>devine</LastName></Candidate></Graduates><ExperiencedHires><Candidate><FirstName>paul</FirstName><LastName>devine</LastName></Candidate><Candidate><FirstName>Meera</FirstName><LastName>Bhana</LastName></Candidate></ExperiencedHires></DataExtract>'

select @SQL

select CAST(@sql as xml)