i don't know which one to choose

which one to choose是wh- to do 结构，不是从句。
1.该结构起名词作用，作主语、宾语、表语、同位语。
I didn't know how to choose .

2.wh-词如果是副词，如where\when\how等，作to do 的状语；如果是代词，如what\whose 等,作to do 的宾语或宾语的定语。
I don't know which book to choose.
I don't know what to choose.

宾语从句在动词后面如果有疑问词
，用疑问词＋不定式to,这是固定用法
同样做CHOOSE的宾语

which one是 choose 的宾语
这个名字的结构是
I didn't know which one to choose .
主语 谓语 不定式做宾语