c - When is it necessary to allocate dynamic memory using malloc on pointers?

I am having trouble fully understanding the malloc() function in C, more precisely when it is necessary to use it.

When I declare a pointer to a global struct like so,

struct Position* currentPositionPtr;

do I need to assign dynamic memory to it using malloc to initialize it?
Or is it good practice to simply assign a pointer of the struct to it later on when needed like e.g.

currentPositionPtr = getPosition();

where getPosition() returns a pointer to the "struct Position".

Answer

What does getPosition() do?

If it returns a valid pointer to struct Position, then of course you don't need to allocate memory for the struct twice. I hope your function does not look like this:

struct Position *getPosition()

{
    struct Position p = { x, y };
    return &p;
}

since this would exhibit undefined behavior (by returning a pointer to a block scope automatic object). Generally, you rather return an already malloc()ated pointer instead:

struct Position *getPosition()
{

    struct Position *p = malloc(sizeof(*p));
    p->x = 42;
    p->y = 1337;
    return p;
}

Then, again, you don't need an additional call to malloc().

If, however, it's not the called function who is responsible for the allocation, then, well... it's the caller who is:

void getPosition(struct Position *p)
{
    p->x = 42;
    p->y = 1337;
}

And in this latter case you would need to call it like this:

struct Position *p = malloc(sizeof(*p));
getPosition(p);

if you need your struct to survive function returns, or

struct Position p;
getPosition(&p);

if you don't.