If you want to add something before the "Proceed to Checkout" button on the cart screen in the Shopify theme "Dawn", there is no block element you can add, so here is an alternative using a customized Liquid section and Javascript.
Example of settings for displaying HTML just before the "Proceed to Checkout" button on the cart screen of the "Dawn" theme (when using only the theme editor without editing the code)
[How to set it up] Add a "Customized Liquid" section to your cart screen template and insert the code.
