Question

I do not know when I should -ing form. By example: I want to know..., or I want knowing...?

Answer 1

-ing is usually used as a verb, something that is happening right now.  For example, "I am driving to the store" or "I am talking to you."  Sometimes it is used as an adjective to describe a noun like, "Drink from the running water" or "Speak to that working man."  In your example, it would be either "I want to know." or "I want a working knowledge."

Answer 2

Thanks, Aegelis. But what happen when -ing is a noun? I confess you this issue is confusing for me.

Thanks again,

Guido 

Answer 3

I see. I suppose there's no change, like in these sentences:

1.    Seeing is believing.
2.    Reading that book was very interesting.
3.    Drinking is essential
4.    Drinking too much pop can make you fat.
5.    Taking the bus was rather a good idea.
6.    Swimming is very good exercise.
7.    Taking too many aspirins is dangerous.
8.    I really like sailing .
9.    This article really needs rewriting.
10.    He drove two hundred miles without ever stopping.
11.    I look forward to seeing  you again next week.
12.    I'm thinking of painting my house.
13.    I started by carefully turning off the electricity
14.    Do you mind shutting the window, please ?
15.    Will you consider taking the job?
16.    I've really enjoyed meeting you.

Source: http://linguapress.com/grammar/gerunds.htm

Answer 4

For describing feelings use verb-ed Ex. I'm bored (I feell bored) For describing a person, or thing as an adjective use verb-ing Ex. I'm boring (because, to talk with me can be bored) Ex. That movie was interesting