On this page of the guide to Halo Infinite, you will find the location of the 10th skull - Famine. It's a secret to be found during exploration of the open world, specifically in the part of the Zeta Halo visited in Act Reformation. We've posted detailed instructions on how to get to skull number ten.
Location of the 10th skull - free exploration
This skull is a bit different because you can find it while exploring the open world. It's not found in a location associated with any of the main missions.
The skull can be found on an island in the south-east corner of the Zeta Halo ring. The island neighbors the area you'll visit for the first time during the Reformation chapter.
Using an aircraft is highly advisable, otherwise you may have problems making the jump off the "mainland" to the island where the collectible awaits. You can accumulate 2,600 valor points to summon a Wasp at any FOB or steal a hostile Banshee. You can find more information on the page Aircraft - how to get?.
Now that you have an aircraft you can simply fly to the island. Circle it until you notice a corpse on the shelf pictured above.
Land the aircraft or jump out of it, reaching the skull.
Famine skull - how it works
The skull causes defeated enemies to drop less ammo. This forces you to switch weapons more often or constantly resupply at ammo crates.