How to build disassemblable structure?
Before you consider the attachment mechanisms, you need to consider the structural design. There is a problem with the current version if it is intended to be load bearing.

A structure that is basically a vertical parallelogram is inherently unstable. The joints serve as pivot points and the top of the structure can effectively slide sideways and collapse. 

A standard approach is to create a triangulation that prevents a sideways shift. This can be done with narrow structural members set on an angle or with a side panel attached at multple points or rigid attachment to at least two walls (or a combination of these items). Any of these techniques can prevents side shift.

In your design, you really need at least two non-opposite sides with this bracing, and preferably all four sides.

Once you do that, there are numerous techniques for attachment. A relatively easy one is the use of t-nuts



Bolt holes are drilled through two members, a t-nut is placed on one side of the hole and a bolt and washer on the other. The t-nut is embedded in the wood and the bolt can be removed with a simple wrench.