What should I expect in terms of cash requirements when flying from Laos to Thailand on Lao Airlines?

Do they require showing cash or will they accept a bank book...

Am confused - as an American, you would never receive a visa on arrival. You could enter visa exempt, but that is different and doesn’t require photos etc. also, not clear, are you having issue flying to Lao or flying back to Thailand?

FYI— This has nothing to do with Thai E–Visa's, Thai Visa Exemption free stamp (ผ.60-ม.17), or even the 15 countries eligible for Thai Visa on Arrival (Thai VoA)

The Lao Airlines (QV) check-in counter staff at Suvarnabhumi Airport have been known to be quite zealous and going beyond their assigned duties as only hired ground staff for an airline and they are NOT Lao Immigration Officers/Officials....

Thai Airways (TG) or Bangkok Airways (PG) at Suvarnabhumi Airport or Thai AirAsia (FD) at Don Meuang Airport are not as zealous as sometimes the Lao Airlines (QV) check-in counter staff at Suvarnabhumi Airport can be about Lao Entry requirements

Alternatively, you can catch a domestic flight to Udon Thani (UTH) and make an overland crossing at the Friendship Bridge land border (Nong Khai)

or, catch an overnight train from Krungthep Apiwat Central Train Station at Bang Sue (Bangkok), either the train going to Khamsavath Station at Vientiane, or the more comfortable train to Nong Khai, then a short wait for and catch train that goes to Khamsavath Station in Vientiane at Nong Khai Station

The price for a Lao Visa on Arrival (Lao VoA) is USD $40 Dollars (using pristine "new" condition US Dollar Banknotes) for all passports except China and Vietnam, and, there are a few countries that cannot obtain a Lao VoA and must get a Lao Visa Sticker from a Lao Embassy/Lao Consulate beforehand

Also, regarding the price of a Lao VoA, any other currency used is at the discretion of the Lao Immigration Officer issuing a Lao VoA and will not be at a favorable exchange rate price, such as ฿1900 Thai Baht (vs. e.g., ฿1200 or ฿1300 Thai Baht at current exchange rates for USD $40)

Strange that the airline asked, typically that's immigrations job. Can't you show a bank account app with the cash in it? 10K baht is pocket change, you really don't have it handy?

Entering Thailand on a visa exempt stamp you can be required to show 20k baht or equivalent in another major currency IN CASH

When entering Thailand, they sometimes ask you to show 20k thb to prove you can support your stay. Evidence of being able to pay for your stay is pretty normal, though it’s usually immigration and not the airline. However, airlines are held accountable so the do sometimes ask for documentation and etc.

Are you coming on in a visa? A visa exempt? Fyi as an American you don't get visa on arrival. The immigration can ask for evidence of cash so maybe that's why airline asked.