Sources for controller careers
Start with the employer's own recruitment page and the vacancy notice it links to. Then read the medical standard named in that notice.
If the notice points to the aviation authority that issues the licence, read that text as well. A page on this site does not replace those documents. How to read a notice is covered under Recruitment.
These organisations publish material for their own operations. The link is to the organisation, not to a promise that a campaign is open.