Existence of transfer function
You need to determine an expression for the samplers. Normally i would think that those are A/D converters, but  they give $A(s)$ and in the variable $s$ it is implied (sort of) that is the laplace transform, and laplace transforms are used for continuos time systems, so the samplers T could also be just converting the signal into a piecewise constant signal, and that is a non linear operation.

Please try to clarify this, and then we will be able to help you more easily.