What is a synonym for knowledge sake?

There isn't one perfect synonym for "knowledge sake" as it implies a specific motivation. However, depending on the context, you could use:

For the sake of learning:

* For educational purposes

* To expand one's understanding

* To gain enlightenment

* Out of curiosity

* To satisfy intellectual curiosity

For the sake of knowing:

* For the sheer joy of knowing

* To increase one's wisdom

* To become more informed

* To acquire knowledge

Ultimately, the best substitute will depend on the specific meaning you want to convey.