If the linoleum is well adhered, many times it is possible to tile over the existing flooring.
If not, I would suggest scraping it clean and make sure it is well leveled, if necessary use some leveling compound.
Since I'm not a pro, take this as just opinion, but I would guess you do not need to seal it in any way, just use your mortar to anchor the tiles. Perhaps dampen the existing concrete to prevent it from soaking up moisture from the mortar and preventing it from sticking well to the cement and setting up as strong as possible.