I am presuming that you want answers to your question, and not to have your Notebook entry corrected.

Thank you

Thanks!

Cheers!

That's great.

I am grateful.

I appreciate your help.

Thanks for your help.

Thanks for your time.

The lesson/talk was useful/interesting

That helped.

That was helpful.

That will help me.

I enjoyed the lesson.

I really learned something.

I understand this better now.

I would like to clarify something

Could you tell me again about...

May I ask again about...

I am not sure about...

I have a question about...

I am not sure I understand.

I want to tell you my understanding. Please tell me if I'm wrong.

That's a short list to start. I am sure you will receive a lot of responses.

Great question, Natalya.

I like the words you've chosen -- with more details about the context, I could provide more specific recommendations, but here are some quick ideas:

useful: practical, valuable, enlightening, illuminating

interesting: engaging, fascinating

Clarify: explain in more detail, clear up, specify, illuminate

Btw, "feedback" is non-countable in English.