I have used PL200 and 100 % silicone to do this. Both worked well
Sticky gue
It is a type of glue used for gluing pipes together... (not the type of cement in concrete).
R5 Epoxy is not for concrete, it's a marine glue for use on aluminum and plastic parts.
It's hard to guess, as you haven't said WHAT you are gluing plastic buttons onto.
A lot depends if any weight is going to be suspended on the glue. -If not, I would use a construction adhesive like PL200.
Gluing can disrupt the circuit in the Studios and executives. It can also destroy the plastic shell of the headphones. Most types of glue leave a disruptive smell.
White glue will work for that.
No, most plastics are smooth and non-porous. For wood glue to work well it needs to soak into the materials that it's gluing. It can not do this with plastic, so will seem to stick at first, but will come loose when fully cured.
school glue
by gluing with super glue or Elmer's glue
Sewing buttons on is better than gluing them.
Depends what you are gluing.