Know the process, know the data

Two really different things here: the process and its data.

The process is the thing that "works". The data are the things that the working produces (from both its working aspects and non-working aspects).

You can know the flow of the process without knowing much about its data. You may understand how things move and change but you won't necessarily understand what the data MEANS (or its purpose).

The skill/capability of knowing what the data MEANS is that of the data analyst.

The skill/capability of knowing how the data flows and its consumers is that of the process analyst.

Be both but you'll often have to choose one or the other.

Divide and conquer!