Hint
Note that the rule that the predicate path/2 has to
express is very similar to the rule expressed by the predicate
ancestor_of/2: in the first case, you can get from point X to point Y
by chaining together an arbitrary number of
connected/2 relations, and in the second case, X is
an ancestor of Y if a chain of an arbitrary number of
parent_of/2 relations connects them.
So, path(X,Y) should succeed if X is
directly connected to Y. It should also succeed if
X is directly connected to some Z
from where in turn there is a path to Y.