Actually in English we don't have a one-to-one equivalent for "چندمین ". But when we use it, it should be contextualized. That is, considering what we are trying to say we should utilize different words, phrases, and contexts. Where did he stand in the succession of managers of the institute? او چندمین مدیر موسسه بود؟ Where is your city listed in order of economical importance? شهر شما از نظراهمیت اقتصادی چندمین است؟ ''In order of" or "in ... order" , in phrases such as "in order of priority", "in order of  importance", and "in order of size", and "in alphabetical order", "in chronological order ", and in numerical order" respectively, are good phrases to be used with ''چندمین '' as their translation when used in questions. I hope this helps!