Due to Non-Disclosure agreement, I cannot disclose any questions here. But my advice would be clear all your networking fundamentals, their operations and how can you able to utilize them in real time networking operations and issues. Day to day working operations of VLAN, PVLAN, STP, RSTP, Split horizon, VRRP, HSRP, commonly used routing protocols such as OSPF, MPLS, BGP, RIP, EIGRP, IS-IS, ECMP, SNMP, ICMP, etc. In terms of coding, clear your data structure knowledge in terms of Network Automation, such as explain and code how to configure any of the routing protocols on one to may routers or switches at the same time. So be prepared well with python scripting language, network automation tools such as Ansible, automation libraries like Napalm, Netmiko, Paramiko. I think this would be enough for you to make through it. I was able to crack the interview but since I didn't had any relevant internship or full time experience, they didn't move forward with me, but advised me to get relevant experience for couple of months and reapply. Entire experience was very positive!
I would definitely love to consider Facebook as my future place to work for.