1- First, initially use your hands to tell you about the airflow by removing the PC,s case by feeling how much air is coming out ( exhaust).
2- If you get the low airflow, so must replace the fans that give poor airflow because sometimes this fan is usually present in low-quality products.
3- you can have a clear case lid or some clear plastic taped to one side of the case to use some incense. You can use 3 sticks together and then observe here the smoke travels.
4- airflow meters are also available so that you can place them in various locations with your system.