You can find where to get most data on [inara](http://inara.cz/galaxy-components). For most it is fairly simple. Settlements are tougher and will be the majority of the data guide.
First, you need to find a settlement that has the data you need. I use [this google doc](https://docs.google.com/spreadsheets/d/1IVPYPqXbqC7pYY2UggEXLSO0CMaE0ksZMB2Ejlh0aYI/edit#gid=931478812) which has the expected amount of data you can find from a settlement, but is a bit tough to use. To use it, go to the second tab, click “data” -> “filter views” -> the filter you want. The data is all in acronyms (like Modified embedded firmware is MEF). Find the systems that has what you need and note the settlement type (far left, it looks like M4L or similar). If you copy that to your drive, you have access to a more tools available in it, like custom filters and sorting by distance from you. If you just want settlements that CAN drop it, you can use [this](http://ed.b101010.ru/aul/) site which is much easier to use, but it doesnt give you enough information to tell the difference between a settlement with a drop rate of 0.4 (~4 of that data type for every 10 settlements) and a settlement with a drop rate of 1.6 (~16 of that data type for every 10 settlements).
Once you have the settlement type, you will want a [walkthrough map](https://docs.google.com/spreadsheets/d/1iIz4jB_pv74Sp297n_jQM2CEVRURsSzKqSl3OL1WZB0/edit#gid=639735240) (you will need to make a copy of this one to your google drive to use it) and a [key to read that map](https://drive.google.com/file/d/0B1KCuCIwTETSVFBMdlotRmx3LTg/view). Some of the easier settlements (those without restricted zones) you won’t need the map for, but the map will make the tougher settlements MUCH easier (and those same settlements are generally MUCH more rewarding).
To find your walkthrough map, you will want to enter your settlement type into the orange boxes. Your settlement’s acronym stands for [Size][Economy][Security], so a M5H would be medium size (++), type 5 economy (military =1, refinery =2, scientific =3, civilian =4, extraction =5, industrial =6), high security (H). Open the “DAP scan map, and follow it. To get the data, you need to scan all the green circles (data points). Occasionally, it will have you scan a blue circle (core data terminal), but those can be skipped as they don’t give data, just some money. The [key](https://drive.google.com/file/d/0B1KCuCIwTETSVFBMdlotRmx3LTg/view) will help you understand the rest.
If you don’t have a DAP scan map (either as it’s not available, or you didn’t need to look up one as the settlement doesn’t have a secure zone protecting the data points), the map on either of the first 2 sites should be enough to find the data points, just look for the solid green dots (the key can show you what the rest of the symbols on the map are).
Do note, when scanning the data access points, when you scan the first one a timer will start (and that time will get added for each data point you scan until you get them all). Once you complete, the timer will go away and you will get your reward. If you fail, it will restart the scanning process and you will need to start over. Once you successfully scan all of them, you can’t scan any of them again until 1 week has passed.