Question

Is there a sequence point between the two assignments in the following code:

f(f(x=1,1),x=2);

Answer 1

The relevant quote from the (draft) standard [6.5.2.2, 10] is:

The order of evaluation of the function designator,
the actual arguments, and subexpressions within the
actual arguments is unspecified, but there is a sequence
point before the actual call.

So for your expression, the first argument (in particular the call to f) could be
evaluated before the second argument; e.g.:

(x = 1, 1), f <sp> call, (x = 2), f <sp> call

Or, it could be evaluated after the second argument; e.g.:

(x = 2), (x = 1, 1), f <sp> call, f <sp> call

[The function call itself can (and most probably will) contain more sequence points (in particular if it contains a return statement).]

Depending on that, there is a sequence point between the assignments or not.
It is up to the platform (“unspecified”).

Since in the 2nd case, you are assigning to x twice between two sequence points, you have undefined behaviour on such a platform.