if you are overriding the huds DrawHUD method then you can access it’s canvas directly through it’s variable called Canvas.
example
.h in custom hud class derived from AHUD
virtual void DrawHUD() override;
.cpp
void ACustomHUD::DrawHUD() {
DrawDebugCanvas2DCircle(Canvas, FVector2D(400, 400), 200, 30, FLinearColor::Red, 6);
}