How can I configure 2 HDMI/DP ports?

Well,, if you check here, https://www.dell.com/en-us/shop/desktop-computers/xps-desktop/spd/xps-8960-desktop#configurations_section and look at the Ports, the base system doesn't have them all. You need to configure the system with an additional discrete video card.

Chose one on a model that can be configured and check the spec's to ensure you got enough. Most add-on cards will come with at least one HDMI and DP port. Seems the base system does not have an HDMI port though, only DP?

The onboard Intel DP port is DP++ so it will automatically detect an HDMI monitor, when a passive DP(PC)>HDMI(monitor) adapter is used. So you can use either DP or HDMI monitor.

If you don't buy a system with an add-in video card:

You can connect an external MST hub to the onboard DP port which will have multiple DP and/or HDMI outputs for multiple monitors.

Or, if your at least one of your monitors supports DP daisy chaining, connect this monitor to the onboard DP port and connect a second DP monitor to the first one for daisy chaining.