What do I need to do to obtain a TM30 registration document from a hotel in Bangkok?

@Matt *****

it's actually not your responsibility, it's the house owner, hotel, landlords responsibility. If you've never been asked for it then don't worry about it. Some immigration offices won't process anything without it ( Phuket) others aren't bothered. It may be that your accommodation had done it for you and you know nothing about it. Have you had reception ask for your passport and departure card? If yes, then they've probably complied with the reporting requirements.

@Ben *************

it's called a TM 30, it registers your place of residence with the Thai govt. Legally, wherever a foreigner stays is obligated to inform the govt within 24 hours, so they can keep track of foreigners. Practically, the only time you need it is if you go to immigration asking for something like an extension of stay.