I really like to work with my mentor, who always works effectively and productively.

When I work with him, I can learn a lot of things and getain many insights ofrom works.

Because he wanted to introduce us to more things foto better understanding a wor a task, he showed us a presentation file.

It had many charts and diagrams that I couldhelped me understand the goal of the work.

The interesting thing is that he made athe file all at once.

Because he usually thought a lot and gathered ideas, he could make the file quickly.

I should learn aboutfrom this attitude as well.

When I work with him, I can learn a lot of things and get many insights ofabout works.

Because he wanted to introduce us to more things forto help us understanding a the work, he showed us a presentation file.

It had many charts and diagrams thatso I could understand the goal of the work.

The interesting thing is that he made athe file at oncequickly.

Not sure what you're trying to say here

Because he usually thoughtthinks a lot and gathered ideas so, he could make the file quickly.

I should learn about this attitudehow to do this as well.

I really like to work with my mentor, who always works effectively and productively.

Without the added comma, you are indicating that you're talking about one of several mentors - the mentor who works effectively and productively, unlike the other mentors. When you add the comma, it's clear that you just have one mentor, and that mentor is effective and productive.

When I work with him, I can learn a lot of things and get many insights ofabout works.

"Insights of work" sounds like the insights belong to the work. "Insights about work" shows that the insights are yours. Work should be singular here since "work" is a general concept. If you wanted to talk about many smaller parts of your work, you might use the word "projects" instead.

Because he wanted to introduce us to more things forto help us understanding a the work, he showed us a presentation file.

"A" doesn't go before "work" in most cases. The exception would be if the work was a specific item, like a work of art.

"For understanding" just sounds unclear in your sentence, so replacing it with "to help us understand" is more clear.

You need to put "to" after "introduce" unless you are focusing on the thing/person being introduced. For example, you would leave out "to" if you said, "I should introduce Sandra," or, "The company introduced its newest product," because those phrases leave out who is being introduced to Sandra or the product.

It had many charts and diagrams so that I could understand the goal of the work.

If you are saying why your mentor had charts and diagrams, you need to add "to." "To" indicates that you are explaining his reason for doing it. Without "to," you are just saying that you can understand the charts and diagrams, but it makes the end of the sentence ("the goal of the work") stop making sense.

The interesting thing is that he'd made athe file at oncequickly.

If you say, "He made a file at once," it sounds like you're saying that he made the file while he was in the meeting with you. If you say, "He'd [he had] made the file at once," then you are saying that he made it before your meeting.

Changing "at once" to quickly just sounds more natural. If you use "at once" it sounds like you're focusing on when he started making it, not how efficiently he made it.

It meant thatThat's why he already had a lot of materials.

You can leave the sentence the way it is, but it doesn't sound natural. I changed it to something that sounds more natural.

Because he usually thought a lot and gathered ideas, he couldthinks a lot and already has so much knowledge, he was able to make the file quickly.

Your sentence isn't grammatically wrong, but it sounds unnatural.

I should learn more about tdeveloping his attitude as well.

If you say you should learn about his attitude, it means you want to learn about what his attitude is. I think what you actually want is to learn how to have an attitude like his. (How to develop the attitude in yourself.)