Here is a good article that describes how to debug a batch job in AX2012 : https://dynamicsaxinsight.wordpress.com/2014/03/10/ax-2012-how-to-debug-batch-jobs-and-service-operations/
Category: Debug
AX – D365FO – How To Load D365FO Debug Symbols #D365FO
While debugging Visual Studio not stopping on your breakpoints? This could be that your D365 debug symbols are not loading. There are several settings that need to be set correctly to allow D365 debug symbols to load. This article will explain how you can troubleshoot this issue (see below) https://dynamics365musings.com/loading-d365-debug-symbols/
AX / Dynamics 365 For Finance and Operations blog 