What specific adapter should I use to connect 2004 Apple Cinema Display to 2019 i9 MacBook Pro

As already indicated, you will need a USB-C to DVI adapter. There is something important you haven't told us: the screen size of that display. If it is the 20-inch or 23-inch model, it has a resolution that is within the limits of single-link DVI. If it is the 30-inch model, you'll need to look for an active USB-C to dual-link DVI adapter, and use a dual-link DVI cable (if that display does not have a permanently-attached dual-link DVI cable). Single-link DVI does not have the bandwidth to support the 30" Cinema Display's 2560x1600 resolution, so using a single-link adapter (or cable) would cause the monitor to fall back to some lower resolution.

If the monitor has software-controlled brightness (as some Apple monitors do), you may also need to make a USB connection in order to be able to adjust the monitor's brightness.

The 2004 Apple Cinema Displays have DVI inputs.

You’ll need a USB-C to DVI adapter to use it with the 2019 MacBook Pro that has Thunderbolt 3/USB-C ports.