Sometimes I go back to look for a job posting that I saw on the previous day, but it just isn't there. Even trying to find it using advanced search doesn't help. Do some jobs just disappear for some reason? This one certainly didn't seem to be against policy or anything.
You should be able to Save a job post that interests you by clicking on the heart button on your job feed, or the "Save Job" button on a job post. You can access it by going to your Saved Jobs page (Find Work > Save Jobs).