A, P, R, X, S and Z are sitting in a row. S and Z are in the centre and A and P are in the ends. R is sitting on the left of A. Then who is sitting on the right of P?

There are $6$ positions in total in a linear row: $\underline{1}\underline{2}\underline{3}\underline{4}\underline{5}\underline{6}$.
1. "S and Z are in the centre" $\to$ Positions 3 and 4 are occupied by S and Z (in either order: S, Z or Z, S).
2. "A and P are in the ends" $\to$ They occupy positions 1 and 6.
3. "R is sitting on the left of A" $\to$ For R to be on the left of A, A cannot be at the extreme left end (position 1). Therefore, A must be at the extreme right end (position 6), which means R is at position 5.
4. Consequently, since A is at position 6, P must be at the extreme left end (position 1).

Now we can fill the layout:

* Position 1: P
* Positions 3 & 4: S / Z
* Position 5: R
* Position 6: A

The only remaining letter is X, which must occupy position 2.
The complete configuration is: $\text{P}\text{X}(\text{S/Z})(\text{Z/S})\text{R}\text{A}$.

Looking at the position immediately to the right of P (position 2), we find X.