Use the following text string on the web client search page "{_stateWorkflowId_:(com.ibm.ram.legacy)" (without the quotes). This will return a list of assets using legacy review process. You can sort the list based on community and see all the communities that have assets using legacy review.

The effort to migrate from legacy to lifecycles can vary a lot. Their are many things to consider such as creating the master lifecycle(s) and community lifecycles inherited from the master ones that match all the conditions of the current legacy review processes. Putting the lifecycles in the correct order on the community lifecycles page. Ensuring the policies are applied to all the states in the lifecycles you want to run since legacy processes run in all states whereas policies are specific to lifecycle states. Ensure reviewers are put on specific states in the lifecycles. Ensure advanced settings are set on the lifecyce based on previous visibility of legacy process. Also assets migrated to lifecycle process will start in first state once moved over.