Hi there, you should use the FPaths class, which provides various useful methods for dealing with paths. Specifically, you can use FPaths::ProjectDir() to get the directory of the project or FPaths::ProjectContentDir() to get the content directory of the project.
Getting the Project Directory
#include "Misc/Paths.h"
FString ProjectDirectory = FPaths::ProjectDir();
UE_LOG(LogTemp, Log, TEXT("Project Directory: %s"), *ProjectDirectory);
Getting the Content Directory
#include "Misc/Paths.h"
FString ContentDirectory = FPaths::ProjectContentDir();
UE_LOG(LogTemp, Log, TEXT("Content Directory: %s"), *ContentDirectory);
Hope this helps.