This is a great question in any programming language and is really designed to see how you problem SOLVE. You're not given much INFORMATION, but some interviews will slip you more details of the ISSUE as you go along.

Start SIMPLE:

• get the exact steps to reproduce it.
• find out the device, iOS version.
• do they have the latest version?
• get device logs if possible.

Once you can reproduce it or have more information then start using tooling. Let's say it crashes because of a memory leak, I'd expect to see SOMEONE suggest using Instruments leak tool. A really impressive candidate would start talking about writing a unit test that reproduces the issue and debugging through it.

This is a great question in any programming language and is really designed to see how you problem solve. You're not given much information, but some interviews will slip you more details of the issue as you go along.

Start simple:

Once you can reproduce it or have more information then start using tooling. Let's say it crashes because of a memory leak, I'd expect to see someone suggest using Instruments leak tool. A really impressive candidate would start talking about writing a unit test that reproduces the issue and debugging through it.