A triggered WebJob can handle its own logging and can be accessed by selecting your triggered WebJob then selecting logs as shown.
Logging in a continuous WebJob is a little trickier. This is because there is technically no endpoint, as soon as it finishes running it runs again. With a triggered WebJob you have a set start and finish which creates a distinct set of tracing information for each run. There is no distinct start and endpoint in a Continuous WebJob, therefore logging will require a different system. This logging system is Blob storage. To create a Blob you must first create a Storage Account.
To create a Blob go to your Storage Account and select Blobs > + Container (essentially new) > then select a name for your container (Blob) > click ok.
You have now created a Blob.
Go back to your App Service and select Diagnostics Logs (under Monitoring).
Update application logging to be enabled, for the storage settings select the Blob you just created. I would also suggest that you define a retention period for your logs otherwise they will not be deleted.