The best metric for a network administrator to check is hop-by-hop network latency. This is because network latency is the time it takes for a packet to travel from the source to the destination, and it affects the loading speed of web pages. Hop-by-hop network latency measures the latency between each pair of routers or switches along the network path, and it can help identify where the delay is occurring. By checking the hop-by-hop network latency, the network administrator can determine if the problem is caused by a slow or congested link, a misconfigured or faulty device, or a routing issue.
Jitter is the variation in latency over time, and it affects the quality of voice and video applications. Jitter does not directly affect the loading speed of web pages, and it is not a useful metric for troubleshooting this issue.
Server interface CRC errors are errors that occur when the cyclic redundancy check (CRC) of a packet does not match the expected value, indicating data corruption. Server interface CRC errors can affect the reliability and integrity of data transmission, and they can be caused by faulty cables, connectors, or interfaces. Server interface CRC errors do not necessarily affect the loading speed of web pages, unless they are severe enough to cause retransmissions or packet loss.
Server NetFlow data is data that is collected and analyzed by the NetFlow protocol, which monitors and reports on network traffic flows. Server NetFlow data can provide information on the volume, type, and direction of traffic that is sent or received by the server, as well as the source and destination IP addresses, ports, and protocols. Server NetFlow data can help identify network usage patterns, trends, and anomalies, but it does not measure the latency or performance of the network.
Reference
What is Network Latency and How to Measure It
How to Troubleshoot Network Latency Issues
What is Jitter and How to Measure It
What is CRC Error and How to Fix It
What is NetFlow and How Does It Work
CompTIA Network+ Certification All-in-One Exam Guide, Eighth Edition (Exam N10-008)

Routing is the process of forwarding packets from one network to another, based on the destination IP address1.
Routing occurs at the network layer of the OSI model, which is the third layer from the bottom2.
The network layer is responsible for logical addressing, path selection, and packet delivery across multiple networks2.
Routers are the devices that operate at the network layer and perform routing functions, using protocols such as RIP, OSPF, EIGRP, or BGP23.
The other layers of the OSI model have different roles in the network communication process, such as:
The data link layer is the second layer from the bottom, and it is responsible for framing, addressing, and error detection of data packets over a single network, using protocols such as Ethernet, Wi-Fi, or PPP2.
The transport layer is the fourth layer from the bottom, and it is responsible for ensuring reliable, error-free, and ordered data transfer between devices, using protocols such as TCP or UDP2.
The physical layer is the bottom layer, and it is responsible for transmitting and receiving bits over a physical medium, such as a cable, a fiber, or a wireless signal2. Reference:
1: CompTIA Network+ N10-008 Cert Guide, 1st Edition, Chapter 5: Routing, p. 179
2: CompTIA Network+ N10-008 Cert Guide, 1st Edition, Chapter 1: Introduction to Networks, pp. 22-29
3: CompTIA Network+ N10-008 Cert Guide, 1st Edition, Chapter 5: Routing, pp. 180-191

tracert is a command-line tool that can trace the route of a packet from the source to the destination. It can show the number of hops, the IP address and hostname of each router, and the round-trip time for each hop. tracert can help the technician troubleshoot the unreachable website by identifying where the packet is dropped or delayed along the path. ipconfig is a command-line tool that can display and configure the IP settings of a network interface. arp is a command-line tool that can display and manipulate the Address Resolution Protocol (ARP) cache, which maps IP addresses to MAC addresses. netstat is a command-line tool that can display network connections, routing tables, and statistics.

802.11 ax is the latest wireless standard that operates in both the 2.4GHz and the 5GHz bands. It offers higher throughput, lower latency, and improved efficiency compared to previous standards. It also uses technologies such as OFDMA and MU-MIMO to reduce interference and increase capacity in dense environments.
Therefore, 802.11 ax is the best choice for a wireless network in an office building with high saturation on both bands.
References
* Part 3 of current page talks about the benefits of 802.11 ax and how it improves network performance in congested areas1.
* CompTIA Network+ N10-008 Exam Cram covers the wireless standards and their characteristics in Chapter 5. It also provides practice questions and explanations for the exam.

MTBF is the disaster recovery metric that describes the average length of time a piece of equipment can be expected to operate normally. MTBF stands for mean time between failures, which is a measure of the reliability and availability of a device or system. MTBF is calculated by dividing the total operating time by the number of failures that occurred during that time. MTBF indicates how often a device or system fails and how long it can run without interruption. A higher MTBF means a lower failure rate and a longer operational life span. References: [CompTIA Network+ Certification Exam Objectives], What Is Mean Time Between Failures (MTBF)? | Definition & Examples | Forcepoint