पूछताछ  =  enquiry
I've been making inquiries about the cost of a round-the-world ticket.

जाँच-पड़ताल  =  investigation
Two men are helping the police with their inquiries

जाँच  =  question
There was an inquiry about my training

अन्वेषण  =  research
They are doing more inquiry on men's attitude

जाँच  =  search
The police conducted a long inquiry for the lost child

सर्वेक्षण  =  survey
There is some need of inquiry at slums