Its different for every engine, model, and make of car why dont you narrow your question down and add some important details that can help someone answer it with something you can use
On a 1979 Dodge Power Wagon with a 360 motor, the number 1 peg on the distributor cap is typically located at the front of the cap, aligned with the engine's front. To locate it accurately, you can trace the spark plug wire from the number 1 cylinder, which is the driver's side front cylinder. Make sure the engine is at top dead center (TDC) on the compression stroke for the number 1 cylinder to ensure proper timing alignment.
The marked # 1 position on the distributor cap faces towards the REAR
Number 1 on the distributor cap is the top post closet to the firewall. Looking at the distributor cap it would be... top row 1-3 bottom 2-4
where is number one on a vortex 4.3 v-6 distributor cap
The distributor cap should have the number 1 marked on it. The distributor cap is installed with the # 1 position facing the engine , slightly towards the drivers side of the engine
Front righthand side of cap
Should have a small number 1 on the top of the cap.
# 1 on the distributor cap faces to the FRONT / CENTER
# 1 on the distributor cap faces to the FRONT / CENTER
The marked # 1 position on the distributor cap faces to the FRONT
The marked # 1 position on the distributor cap faces to the FRONT
in number 1