"Anyone know the audit object in universe whioch gives failure reason?"
I believe and pretty sure that there is no such object which would give a faiure reason. Some logic I thought would be what would happen if report instances are success, In this context there would not be any specific reason 
I speculate that there can be some sdks to create a webi / cr' made to fetch the error contents along the record of reports getting failed. Alas I am no expert in SDKs.
In a Nutshell, I dont think the functionality would be available in audit for reason of failed instances.