どんな vs なんの
 

when i want to ask what kind of tempura is it?

do i say どんなてんぷらですか
or なんのてんぷらですか

what's the difference between the two?

It's どんなてんぷらですか。 This is 'What kind of Tempura is it.' I'm not sure if your second sentence really means anything, you'd need to wait for a native speaker. Also, this was mentioned in another thread, but you should really just put your answers in our 'Japanese Help Questions/Translations' thread. There's no need to make a different thread each time, and you'll still get answers to all your questions if you post in that thread. Don't take this is angry, it's just a suggestion.

Edit: I saw that you realized this in another thread. ^^; Sorry, feel free to disregard the latter half of my post!

Pardon the romaji

isn't donna "what kind?"
and nanno what is?

nan no imi? what's the meaning
donna (no) imi? what kind of meaning?

This isn't nearly as easy as other Jaapnese learners might tell you.

なんのてんぷらですか can only mean one thing and it's easy to use.

Tenpura can be made with many different food items, all types of seafood, and vegetables and such. Suppose there's a piece of tenpura in front of you. You know it's tempura from its look but you don't know what's inside the batter. This is when you say なんのてんぷらですか.

どんなてんぷらですか , trust me, isn't too easy to use.

Suppose someone is telling you about the tenpura he ate in Tazewell, Tennessee. The town has no Japanese population and it has little connection to anything Japanese whatsoever. You know a lot about tempura and Japaense culture in general. You want to know how the Tazewell tenpura looked and tasted even though you already know you're going to hear a horror story.:) This is when you say どんなてんぷらですか.
_________________

Another meaning of どんなてんぷらですか is the same as なんのてんぷらですか. However, if the tenpura is right in front of you, you don't say どんな. You say なんの. This is super-important.

You use どんな when you ask someone who ate tenpura not too long ago about what varieties he had.

This is an excellent explaination. But to the OP, do not get too caught up trying to remember every little difference. At some point it is probably more effective just to listen to how native speakers talk, and repeat it just like they say it, and when they use it.

ok i'l try to listen to how native speakers talk and mimic, anyway sashimister that's a very gd clarification, i think i understand abit now many thanks

And what about "What sport do you play?".
I hear japanese people saying "どんなスポツをしますか。" Why can't I say "何スポツをしますか。"?

Edit to remove idiocy
I
I did
I did this
I did this to
I did this to hit
I did this to hit the
I did this to hit the word
I did this to hit the word limit.

1. You revived a dead thread.

2. The word is スポーツ.

3. The "real" reason that we do not say 何スポーツ is that we just don't. In Language, that is simply the most valid reason.

The more superficial reason is that 何 is a pronoun and you just cannot directly combine a pronoun with a noun. You can say 何のスポーツ but it will not sound as natural as どんなスポーツ.

4. In case you alreay know words like 何色 and 何語, those are fine because they are each "one word".