關於這句英文的文法？

to wear是不定詞，當動語know的受詞，所以是名詞性質。可以接受前面形容詞what的修飾，和後面介系詞片語for party的修飾。
what當形容詞去配名詞的用法可參看下列的句子：
What time is it?
What books did you read during the vacation?
What day of the week is it today?

2009-03-03 11:26:06 補充：
如果你把what當成代名詞來看，to wear當成修飾它的不定詞（屬形容詞性質），也是可以的。因為what就成了動詞know 的受詞了。因為文法分析有時可以找到不同的解釋的。

2009-03-03 16:26:56 補充：
對不起，我前面的判讀有錯。to wear是不定詞，是屬於動詞衍生的詞類，所以只接受副詞的修飾。what不能做副詞用，所以應該是當代名詞。所以我最先的判斷是錯的。what應當成I don't know的受詞，to wear是受詞補語。介系詞片語for party修飾to wear. 可以想一下類似的句構的關係：I don't want you to leave.有受詞補語to leave

2009-03-03 16:31:18 補充：
類似what to wear的片語還有how to do it, when to go, where to go

what to 什麼
Wear 穿; 戴着, 佩, 留着(胡须等)
1. I'll have to think what to wear.
2. 我还得想一想穿什么衣服。
3. First I had to decide what to wear.
首先我得决定穿什麽衣服.
4. I have not decide what to wear.
我还没决定穿什么衣服。
5. What are you going to wear, Sandy ?
桑迪，你打算穿些什么衣服？
6. What are you going to wear today?
今天你准备穿什么衣服?
7. What is you go to wear, sandy?
桑迪，你打算穿些什么衣服?
8. I have not decided what to wear today.
我还没决定今天要穿什么衣服。
9. What should I/ought I to wear for the banquet?
参加宴会我应该穿什么？
10. If you are to attend the banquet, what will you wear
如果你要出席宴会,你会穿什么
11. If you is to attend the banquet, what will you wear.
如果你要出席宴会,你会穿什么。

因為有"去"這個字啊
WEAR是穿的意思

I don't know what to wear for party.
=I don't know what I am going to wear for party.
=I don't know what I am gonna wear for party.
未來進行式之省略語
be going to +V的句形比will.shall,在口語上更常用

因為你已經有一個動詞 know 在前面
所以後面那一個動詞要加 to

to wear的意思想表達的應該是為了要去宴會而打扮,所以to就是依照此宴會來打扮我的穿著~~

整句應該是
(我不知道為了這場宴會,我應該要做什麼樣的打扮 )