It sounds like you have the basic skills to start learning QlikView and/or QlikSense. If your source data exists in databases instead of excel files, then basic sql knowledge will be helpful and you will need to know how to set up an odbc or oledb connection to a database. If you have a lot of data from different sources then knowledge of dimensional modelling will be useful. Other than that you need the discipline to read documentation like help files, reference manuals, tutorials, etc.
Professional classes can help you get up to speed fast. So if your time is limited and your budget allows it then following a Qlikview training will likely be a good investment. If you're more inclined to do self-study then there are free tutorials and training you can follow (see New to Qlik Sense and New to QlikView) and a number of books you can use. https://www.packtpub.com/big-data-and-business-intelligence/qlikview-11-developers is a very good book to start with. It's on offer at the moment for $5 / €4.80.
Gysbert's response is a good one... but you do not need formal classes. My suggestion, download the free version and watch the tutorials on the Qlik site to get something up and running. After that go to YouTube and watch the free videos about how to use the software. If you know a little SQL, it will take you a long way. The Expression formulas are the trickiest. I have 6 different manuals/books on QV and the one I use the most is from the "Masters Summit" - they handed out a hard copy work book and examples of everything they covered during the summit. So spending a lot of money on books won't get you as far as watching some of the YouTube videos. These are made by consultants that implement QlikView. They always show load script and expression examples that will give you the real info that you need and explain why it works. Once you have played with the software, you will get hooked and then really want to go to a Masters Summit. Having some experience in the software before you go will really help.
A day doesn't go by that I don't google "QlikView and my question" - just type QlikView before your need and lists and lists of Q&A, examples ... come up. It's fab! Join the Qlik Community and ask a question if you need to. Very helpful people answer almost immediately if you provide enough information as to what you are trying to do.
The only thing that I haven't been able to do is export a quote and comma delimited CSV file properly. (i.e. You get no quotes and commas or triple quotes and commas. )
There is so much you can do with this software - it is really worth taking a serious look!
Author Note: we use the QlikView version.
My advice is really understand how the Associative Model works in Qlik (QView and QSense are the same).
Get this correct and development of your docs/apps will be a lot easier, I have seen some models that
are somewhat messy and as such the dev has to write some tedious and incomprehensible expression
logic to arrive at a result due to a bad model design.
If you are using business data along a timeline, then make sure you have a calendar table in your model
that can handle Fiscal periods, it's worth the effort here as then building time/date (e.g. TY,LY etc) into
expressions e.g. Set Analysis is significantly easier.
Tip: If you are relationally minded (e.g. SQL, Oracle etc) you will need to adjust your thinking for the Associative model.