Your code looks incomplete and you're posting small chunks of it from time to time but I believe this syntax is what you want:
#include <iostream>
using namespace std;
template <typename P>
class Stack {
public:
template <typename X> int pop(X pred) const;
};
template <typename P>
template<typename X>
int Stack<P>::pop(X pred) const{
return 0;
}
int main() {
Stack<bool> obj;
char a;
obj.pop(a);
return 0;
}