Cleaning and Reattaching Sink to Marble Surface Drainage and wastage systems and plumbing help, advice and answers

[mcnof]

I’ve got a porcelain sink that’s completely detached from a marble surface. It’s perfectly balanced so is not in any danger of falling off, only if you lean on it! I’d like to clean the residue off and reattach. What materials do I need and what’s the best process? Thanks!