How to stick oreo biscuits together to make a tower?

I'd recommend that unless you're just stacking oreos on top of each other, that you use something else for structure and then afix the oreos on using icing as a mastic.

Typically, you'd use one of the following:

• A hollow structure made of gingerbread sheets, fastened together
• A bit of dense cake (eg, pound cake), cut down to the proper size
• Rice crispie treats, formed into the size you wanted

Personally, I'd go with the rice crispie treats, in part because you can just use that without any oreos. (you can either take a handle of a spoon or similar and press in the texture you want once it's mostly but not fully set).

... but you can also deal with the texturing on the fondant ... just roll the fondant out a bit thick, apply it, and then use something appropriately sized and smooth (no sharp edges) to press in the grout lines. If you have clay working tools, use those, but also the back edge of some table knives will work. You have a longer working time than trying to do this on rice crispie treats, you just have to be more careful about not tearing or cutting the fondant.

You are going to have to experiment, if you want to use oreos.

The problem is that you need somethign strong enough to allow you to roll the glued together tower in fondant.

I would try, in order:

• Tempered chocolate, if you can do that; its pretty strong when fully cooled
• Royal icing
• Very thick ganache
• Peanut butter

This type of fancy cakes usually has inedible internal supports, such as wood rods. I wouldn't trust the cookies to remain safely upright even after being glued. My intuition would pronounce a glued tower stable if its height is 2x diameter max, anything above feels problematic. It is a different case if you create a hard tower with the cookies somehow embedded in it, but this means we are talking something like embedding cookies in hard candy, which doesn't sound appetizing and probably looks strange. In the end, it will probably work better without cookies.

The alternative would be to create maybe a four corner "basket" out of rods to put the stack inside, and decorate the stocks nicely. In this case, you can use a fairly weak glue, even some whipped cream will be OK, because the glue doesn't have to support the structure.

There are videos on the Internet for creating fancy cakes, often episodes of reality TV shows. You might want to watch them for inspiration. I haven't seen any with a cookie tower, but I have seen 3-D models of stag heads and other sculptures, you can learn a lot from them.