Problem scenario
Some external requests that a Lambda function is making are not working. The Lambda logs indicate that the function is timing out. You want to see what VPC your Lambda function is in. What do you do?
Solution
Log into AWS via the web UI.
Go here (but change "us-west-1" in both places to your VPC's region: https://us-west-1.console.aws.amazon.com/lambda/home?region=us-west-1#/functions/ )
Search for "VPC"
It may be that your Lambda function is not attached to any VPC.