As a scientist, the idea of a "research notebook," or its functional equivalent, has been well ingrained into me. However, it's not clear to me if this is a universal phenomenon, or if it's limited to the sciences.
For students working in the humanities and other fields—such as literature, economics, or philosophy—what is the working equivalent of the laboratory notebook? If not, what is the preferred method of keeping records in those fields?
I think you really need to understand research methods humanities, and this varies field to field.
One (but not the only) approach are Qualitative Data Analysis(QDA) methodologies used widely enough to support a small industry of software vendors delivering (often very expensive) QDA tools. Examples include Atlas-Ti, NVIVO, QDA Miner and Tinderbox.
These tools provide the closest thing I can think of to a 'research notebook' for academics in the humanities.
Understanding what people say is a QDA example in Tinderbox, representative of the sort of work done in QDA tools.