Should I Apply for a Non-B Visa in Denmark or Opt for a 30-Day Visa Exemption Upon Returning to Thailand?

> I just spent 2 months in Thailand getting an English teaching certificate

I have no idea what this is. You need a bachelors degree (or equivalent) to teach in Thailand.

> I got offered a teaching job in a school starting May 15th

Sounds like a government school. Unless the contract was signed already, school is starting early July.

>Would you recommend to start applying for non-B visa in Denmark so that I can travel back to Thailand ASAP

Apply in Denmark, but not too early if the school allows it. You have 3 months from the time the Non-B is issued to the time it expires.

>Or should I go for a 30-day visa exemption upon arrival

You can not work on a visa exemption.

Just so you know, apparently schools in Thailand will be closed until the beginning of July :)

Definitely get it while you’re abroad but check how long it takes and what you need to get it in Denmark.

I'd say have the employer FedEx or DHL you the documents and apply for the 90 day Non-B visa at the thai consulate in your country.