How can I include Adwords conversion code on a thank you page?

Yes it is possible to do this but you will need to create a custom HTML Thank You page in a hosting site. You will then redirect to this HTML page to be used as you Thank You page.

Below is a guide on how you can redirect your HTML Thank You page:

https://www.jotform.com/help/38-Redirecting-Users-to-a-Different-Page

To also mention we have Google Analytic widget which will allow you to track visits and conversions from your page.

https://widgets.jotform.com/widget/google_analytics

Kidly let us know if you need more support.