Is XOR equal to XNOR when odd number of inputs are considered?
The behavior of a a XOR gate with multiple inputs needs to be defined, it is not just a simple extension of the two-input XOR gate. As always with definitions it is possible to have different, even contradicting, ones. 

In my opinion this definition seems to be useful:


  For multiple arguments, XOR is defined to be true if an odd number of
  its arguments are true, and false otherwise. This definition is quite
  common in computer science, where XOR is usually thought of as
  addition modulo 2. In this context, it arises in polynomial algebra
  modulo 2, arithmetic circuits with a full adder, and in parity
  generating or checking. While this means that the multiargument "XOR"
  can no longer be thought of as "the exclusive OR" operation, this form
  is rarely used in mathematical logic and so does not cause very much
  confusion.


The XNOR would just be the inverse of the XOR.