U can use GetCursorPos(&).For initialisation struct use type - POINT. One trick - if u show off cursor, all will work, because cursor will binding camera vector. (GetCursorPos(&) - standart WinAPI function)
If u need get position from ActorComponent with standart UnrealAPI - use:
ACharacter* ownerCharacter = Cast<ACharacter>(GetOwner());
APlayerController* PlayerController = Cast<APlayerController>(ownerCharacter->GetController());
float X, Y;
PlayerController->GetMousePosition(X, Y);
If u need it from standart Character class, use this code (we talk about auto-generate Character class):
APlayerController* PlayerController = Cast<APlayerController>(GetController());
float X, Y;
PlayerController->GetMousePosition(X, Y);