How do I get a Droplet's dedicated IP address?

Droplets do not have dedicated IP addresses, only leased ones.

When a user creates a new Droplet, we lease a static IP address for it from an available pool. This address remains associated with the Droplet until a user destroys the Droplet, at which point the address returns to the available pool.

In addition to the Droplet’s leased IP address, you can create a Reserved IP, which is a publicly-accessible static IP address that you can assign to a Droplet and then reassign to another Droplet later, as needed.

You cannot convert a Droplet IP address into a Reserved IP.
You cannot create Droplets with a specific IP address, but you can use reserved IPs for a static address that you can migrate between Droplets.
You cannot retain a Droplet’s IPv4 when you transfer the Droplet to a new region. Use a reserved IP address to maintain a static IP address.