Final answer:
The correct command for a network engineer to verify IP SLA operations on a congested interface is show ip sla statistics, which provides detailed information about IP SLA operations.
Step-by-step explanation:
A network engineer who needs to verify IP SLA (IP Service Level Agreement) operations on an interface that is experiencing indications of excessive traffic should use the show ip sla statistics command. This command provides details about the IP SLA operations, which can help the engineer identify whether the SLA is being met and if there is any excessive delay or jitter on the network's interface. The options provided in the question do not include the correct answer, but show ip sla statistics is commonly used for this purpose in a Cisco network environment.