VM troubleshooting in most cases means configuration checks on the VM's health or performance analysis. However, there can be several other possible issues, such as wrong drivers, wrong VMware Tools versions, virtual hardware options, and so on.
Objective 7.4 for VCP65-DCV and VCP6-DCV are similar. The title has also changed because there weren't big changes in the troubleshooting approach from vSphere 6.0 to vSphere 6.5. The part on how to troubleshoot virtual machine performance with vRealize Operations has been removed.
The vSphere 6.5 Troubleshooting guide contains in-depth information and examples on this topic: https://docs.vmware.com/en/VMware-vSphere/6.5/vsphere-esxi-vcenter-server-651-troubleshooting-guide.pdf.