try pouring some boiling water on the old adhesive to soften it up then use a wallpaper scraper to get as much off as you can. the more you get off the smoother the floor will be and the easier your tile install will go. If the floor is bumpy you will be fighting with every tile to get them flat and avoid lippage with the adjoining tiles.

Use a modified thinset that is rated for going over cutback adhesive, it should say so on the bag. Dont take just a salesperson's word for it, a lot of them dont know what they are talking about and just want to sell you whats on hand, not what you need to do the job right. If going with a 12" tile use a 1/4" wide x 3/8" deep square notch trowel. You should get about 75 sq ft to a bag.

Thks for your input. Bought a floor scraper and it does the job. Will use modified thinset per your suggestion. Harry

We are having the same problem, chipping the glue away, it's like glass. We are going to be laying swiftlock lamanite wood flooring. We are trying to get it level but having a real hard time