Quality is delighting customers
Can you expand your question ?
-- what phase of testing you are? Integration testing, System testing, UAT or Production?
As a tester first job of you is to log the issue. next call is to attend that issue or find workaround is based on many other criteria's.
is that blocking your testing, is that to be attended by developer immediately to continue your testing further...etc
How often customer uses that area? we can live with that issue for some period of time, if customer usage with that area is very minimal.
If that functionality is max used by customer and no developer is found to attend the issue, you can Try to find out the root cause of that issue - some times it could be configuration issues, where in you yourself can correct and proceed. Some times it could be because of software updates issues, could be missing script issues, could be network issues.
other than its functional / Application issue, as a tester you can apply your experience, knowledge and analyse the logs to find the root cause of the issue and can be fixed or find workaround if its something related to configuration / S/W update issues or compatibility issues.
The best options/answer for this question:-
1. First if developer is not available then you have to inform this critical situation to your immediate supervisor like QA head or project manager.
2. If project manager/QA head is not available in office, then you have to contact them either on cell phone or external email(wait for max half hour if possible)
3. If they do not receive or respond and you have to deliver it to client, then you have to make a clear email or release note to client that what is the situation and how much time will it take to deliver.(Sometimes like developer has left for the day)
4. You can ask and discuss such situation to other team members like tech lead or project manager and try if there is a quick solution like server restart or cache clear from server end
5. Any other developer from other project team who can help you to identify the root cause so that you can specify to client.
Generally in such situations, interviewer just want to know that at how much extent you can control the damage or minimize the loss. So act smartly. For more such details or questions, read the blog:-