Reddit mentions of Getting to Know ArcGIS

My recommended path for you:

1. Work through Getting to Know ArcGIS to understand basic GIS concepts. This book comes with a 1-year ArcMap trial. Some may recommend you use ArcPro but if you are working with large datasets, which is likely as a developer, I would recommend using ArcMap as it performs a lot better in most cases.
   
2. Complete Penn State's GEOG 485 to get to know ArcPy, ESRI's scripting package for Python.
   
3. Complete Penn State's GEOG 863 to get familiar with the ArcGIS Javascript API for making web maps programmatically.
   
   Penn State's courses are free and you can view all of their content without registering for anything. There are a few other courses that would be helpful to you through Penn State, but those two should definitely be the first ones you take. Here's the link to the rest of their open courses if you are interested. I'd also really recommend learning some other data analysis packages for Python like numpy and pandas as well as a database interface like psycopg2.

I've never been to one of these live courses, but I doubt they are any more valuable then just looking at free videos online and reading books. The main advantages to books/videos is you can go at your own pace, they are packed full of more information than can possible be conveyed/received in a short live course, and they are going to be MUCH cheaper.

A couple of good books to check out:

For learning to interact with ArcGIS software: https://www.amazon.com/Getting-Know-ArcGIS-Michael-Law-ebook/dp/B01DK3SWO4/ref=mt_kindle?_encoding=UTF8&me=&dpID=41J4z6t5nqL&preST=_SX342_QL70_&dpSrc=detail

GIS Basics: https://www.amazon.com/GIS-Fundamentals-Geographic-Information-Systems/dp/1506695876/ref=pd_sbs_14_4?_encoding=UTF8&pd_rd_i=1506695876&pd_rd_r=WM4VTBZR7PNZM326YA47&pd_rd_w=3jJcZ&pd_rd_wg=8MKvp&psc=1&refRID=WM4VTBZR7PNZM326YA47&dpID=51oUfZ5VUCL&preST=_SY291_BO1,204,203,200_QL40_&dpSrc=detail

For ArcPy/Python: https://www.amazon.com/Python-Scripting-ArcGIS-Paul-Zandbergen/dp/1589483715/ref=sr_1_1?s=books&ie=UTF8&qid=1517942628&sr=1-1&keywords=python+for+arcgis

There are also plenty of free resources to learn to use QGIS: http://www.qgistutorials.com/en/

The important thing to focus on from any of these sources though, is to learn the concepts, not the processes. The GIS concepts are the same across different softwares, platforms, programming languages, etc.