What's difference between I want and I do want

The meaning is basically the same, but the do adds emphasis.
"I usually don't want my name on doohickeys, but I do want my name on this one."
"I've changed my mind. I do want my name on this doohickey."
"No, I never said that I didn't want my name on it. I do want my name on this doohickey."

exodus74For instance I do want my name should be associated with this doohickeyIf I say this without do what would be change?

Note that "I want my name should be associated with..." is not grammatical. Blue Jay gave your grammatical alternatives.

BarbaraPA exodus74For instance I do want my name should be associated with this doohickeyIf I say this without do what would be change?Note that "I want my name should be associated with..." is not grammatical. Blue Jay gave your grammatical alternatives.

Where can I find rule about it?

I want:
her to come.
my name to be on this.
you to clean this mess up.
him to tell me he loves me.

Do you see the patter here?

Is it possible to say this ?
I do want:
her to come.
my name to be on this.
you to clean this mess up.
him to tell me he loves me.

Yes, if you want to be emphatic.

I don't want him to come, but I do want her to come. (Drawing a difference between what you want regarding "him" and what you want regarding "her.")

A: You don't want to be associated with this, do you?
B: Absolutely I do! I do want my name to be on this! (Emphasizing a positive when it has been suggested that it's a negative.)

Are there any cases where I can't put the do?

You usually do NOT put the "do." It's only when you want to be emphatic that you include it.

understand
thank you