The latest version of WSO2 BPS 3.5.1, does not provide a mechanism to see the execution flow of BPS process. you can understand the flow enabling debug logs of acitivi engine.
Go to <BPS_HOME>/repository/conf/log4j.properties and add the following
But it provides the current state of execution flow with the instance view of WSO2 BPS
login to WSO2 BPS
Go to Main->Manage -> Instances ->BPMN