1. OSB is a stateless and concept of instance is not applicable. So you cannot view running instances in OSB. One of the ways is to use the log action and you should see the statements in the server logs.
Choose an appropriate log level for the different statements and ensure that the weblogic logging level is also set appropriately.
For example: if the weblogic logging is set to ERROR and you try to have a log action at DEBUG level, you cannot see the logs.
if the weblogic logging is set to DEBUG and if you use log action with levels Debug, Info, Warning, Error – all of them will be visible.
If this is only for your debugging the scenarios, you can also enable tracing (in Operation Settings) on the proxy/business service to capture the complete trace of the execution. But ensure this setting is turned off in PROD environments as this hampers performance.
2. The server logs can be found at the following location – MiddlewareHome/user_projects/domains/<your_domain>/AdminServer/servers/<AdminServer or your osb server>/logs
3. You can also use OSB Monitoring to capture the number of messages that were handled by OSB proxy/business service and specific details of how many successful and errored out. Please refer http://docs.oracle.com/cd/E13159_01/osb/docs10gr3/operations/monitoring.html
4. You can use Report and Alert actions to debug your code. Each one has their specific usage. Please refer http://docs.oracle.com/cd/E13159_01/osb/docs10gr3/userguide/modelingmessageflow.html#wp1080496