Is there a way to find out every resource that calls a lambda?
if you want to check from where lambda is calling/using/attached you can check it form designer in lambda.

Dashboard of lambda having designer that show lambda is connected with API Gateway , alexa skill etc.

So you can check everything from designer of lambda although you can also use cloud formation stack if you have made it for lambda.




  Here Lambda is connected with cloud watch and amazon EC2


There should be api gateway and other component also