To research travel documentation and visa requirements I always start with two sources:
 - the [IATA Travel Centre](https://www.iatatravelcentre.com/),  which provides personalised passport, visa and health requirements advice based on your personal details and itinerary.
 - the website of the airline(s) which offer suitable route(s) according to your budget, departure airport etc etc. For example, on British Airways there’s a [Passports,visas and API](https://www.britishairways.com/en-gb/information/passports-visas-and-api) section

If you’re looking at [self-transfer](https://travel.stackexchange.com/questions/171352/do-i-always-need-to-go-through-immigration-if-i-have-a-self-transfer) transit options, remember that typically you may require documents to *enter* the transit country, not just transit.