I'm a little bit confused about the use of On or about in the following sentences:

"thank you for your enquiries ABOUT our products"
or "thank you for your enquiries ON our products"?
and "I took some informations about you" or On you"
(but the former sounds better)
thank you
That's a toughy. I'll try to look it up and see if I can find a significant difference between the two, as I use them both interchangably. At best I would say that taking information about someone could lead to the inference that the information was taken (literally) whereas taking information on someone would likely only lead to the inference that information was recorded about/on the person. On might be just be a shorter form of "on the topic of". I can't verify this right now so make sure to get a second opinion.

PS: Information doesn't take a plural form.
About products sounds better in this context.

If I write a letter to another company, I would ask or inquire about their products.

1) I can talk about pollution of our city.
[Just general aspects and anybody could understand.]

2) He gave us a lecture on pollution of cities.
[ Not necessarily the general aspects and you need some scientific knowledge to understand
some aspects of the lecture.]
Students: Are you brave enough to let our tutors analyse your pronunciation?
Thank you very much!!!!