Can we just showcase static mockups to users and as them to respond to SUS questionnaire? Or, is it good to provide a clickable mockups so that they can get a feel of the workflow?
Do we have any accepted standard practice around this?
The System Usability Scale (SUS) measures the user's perception of usability. Some of the questions are really hard to answer without actually using the system.
Questions 8, 9 and 10 explicitly ask about the user's actual experience with the system. Questions 1-4 could work for mockups as well (but get a slightly different meaning then - asking about the user's expectations instead of experience). Questions 5-7 are about how the various parts fit together, and might difficult to answer with just static prototypes.
So the SUS is best fitted for situations where users can actually interact with the system, and get a feel of the workflow. However, you may not necessarily need actual working prototypes for this - paper prototypes with a facilitator can work as well.