What gym leader can make you use the attack stegngh in Pokemon diamond?

There isn't a Gym Leader in Pokemon Diamond that specifically forces you to use the attack Strength.

However, you'll need Strength to move boulders in order to progress through the game and reach certain Gym Leaders.

For example, you need Strength to access:

* The Gym in Eterna City: You'll need to move a boulder blocking the entrance to the Gym.

* The Gym in Veilstone City: You'll need to move a boulder to access a route leading to the Gym.

While no Gym Leader forces you to use Strength specifically, the ability is necessary for progressing through the game and ultimately reaching them.