How can I execute `getnewaddress` at my full node from a remote server? I have a full node running on a digital ocean droplet. I have an app running at heroku, and I want to execute getnewaddress from this app. I'm trying to generate BTC addresses to which users can send payment to for payment processing in my app. How can I do this? Thanks in advance.

My app is in Python, for what it's worth.
As chytrik said, a better way of generating new addresses on a remote server would be to export an extended public key (xpub) from your wallet and put only the xpub online. Then your private key material would remain offline, and you could generate new child addresses from the xpub using BIP32.

If you still want to execute getnewaddress on your node, you would have to expose the bitcoin RPC by adding server=1 to the bitcoin.conf file on your node in order to accept JSON-RPC commands and call the getnewaddress directly.