There are a lot of ways to accomplish this, and how you implement this kind of management depends a lot on your environment and your requirements.
I've listed out a couple quick options, but I am sure others will chime in as there are many ways to accomplish what you are looking for.
The first thing I'll mention is to take a look at Alteryx Connect. This is a separate product, and has a somewhat larger focus than your initial target of "identify what workflows use a given column/table", but it has some added advantages, like support for technologies beyond Alteryx, a data dictionary that can be easily referenced, a number of data governance capabilities, and in-line integration with Alteryx Designer Search. In my opinion it is worth doing some research on the benefits of this platform.
The second option that I'd suggest is a little more raw, and as such it is not always going to be perfect. For example, if I select a field from a table in a database, but later remove it with an Alteryx Select tool, and never needed the data for processing, the workflow will flag as being impacted, even though the code might work fine, so there is still some manual review potentially required. This might also miss things like a simple workflow which selects data from a table and outputs to a file, if it uses syntax like "SELECT * FROM TABLE", as the column name itself may never appear in the workflow.
With that out of the way: Alteryx workflows are saved as XML documents. As such, you can read and parse these documents using a variety of tools - Alteryx itself is really good at this. As such, it is pretty easy to create an Alteryx workflow which searches a location for all Alteryx workflows, reads them in and searches for column or table names, and outputs a list of workflows that were flagged. You can do this in really simple ways (search the whole document for certain text and output matching workflows), or you can get more complex (search for certain text, but only if multiple search terms are used in the same tool, and try to exclude comments).
There are other methods for accomplishing something like this as well, but these are the two that spring to mind most readily when I think about this particular question.
