If you just need one additional port, use a 2-way splitter. Connect the input port of the splitter using a short coax jumper, attached to the left side of the tube attached to the ground block.

https://www.amazon.com/dp/B07PRYS8YZ?th=1&psc=1

Is this a 2-unit building? Seems like the incoming cable service line is already split somewhere upstream (to the left) of the picture scope … with one line running up to the “PoE” MoCA filter and ground block, and the other line connecting to the input port of the passive 8-way splitter at the bottom of the picture. (FWIW, a non-MoCA CommScope SV8G)

What splitter would work?

For what purpose? For how many locations?

Assuming the one working room is a cable modem location, how many other rooms are you looking to get connected, and for what purpose … cable TV boxes? … MoCA?

Assuming you’re trying to use MoCA, you’d want to use a MoCA-optimized splitter series like that recommended by TomRILReddit, the Antronix MMC1000-B line. Typically, a cascaded splitter setup is used, with a 2-way splitter feeding the modem location and a secondary splitter sized to service the rest of the locations.

You may want to upgrade the pictured “PoE” MoCA filter to a 70 dB model, as well. (Preferably, the “PoE” MoCA filter would be installed on the input port of the top-level splitter, with the filter connected via a short coax line to the ground block.)

These connections would ideally be made inside a protective cable junction box. At a minimum, you’ll want to use weather boots for the coax joints.

Related:

• MoCA-compatible splitter recommendations (… and warnings)
• preferred MoCA filter: PPC GLP-1G70CWWS (Amazon US listing) … 70 dB stop-band attenuation, spec’d for full MoCA Ext. Band D range, 1125-1675 MHz

Wouldn’t the cable pointed to by the arrow be the incoming service to the building since it’s being grounded and that cables goes to the splitter on the bottom right? I’d assume that the bottom cables then go to apartments or rooms in the house.