Look Inside the Cup:
Start by examining the inside of the putting cup.
The side where the grass is more worn or wilted indicates the direction of the grain.
The grain typically grows towards the low spot.

Frayed or Jagged Edges:
If the edge of the cup is frayed or appears slightly jagged on one side, the grain is going in the direction of the frayed edges.
This is where the grass is growing away from the hole and leaning toward that direction of the frayed edge, indicating with the grain.

- With and Against the Grain:
The grain affects the speed and break of your putt.
When putting with the grain (in the direction the grass grows), the ball will roll faster.
When putting against the grain, the ball will roll slower.