www.youtube.com/watch
these guys purposely withheld specific nutrition from the plants and compared to a control plant that was fed properly. This is better than any leaf symptom chart.
I prefer the leaf symptom chart with 'jorge cervantes' name stamped on it -- just to identify it in a good image search, not because i am a fanboy of "jorge." Even so, this video shows some deviations from that chart, which shows just how variable some of this stuff can be. It also goes over the differences of immobile vs mobile - which is also listed in the video above with greater resolution. Some of this stuff is a spectrum and not binary in nature... 'slightly mobile' etc is possible.
The symptoms here seem to be on the outer serated tips and margins and on lower half of plant, which does point toward potassium-related.
more info is needed. Diagnosing purely by leaf symptoms leads to mistakes. some symptoms are not discrete. Nutrients can also inhibit each other just as pH can inhibit availability.
That looks like soil, and adds another layer of unknowns, too. knowing how you fed over time will help eliminate possibiities too. Not knowing what comes with the soil makes things a bit more difficult to assume. in soilless or hydro context, you can track and know exact thresholds relative to your environment for each nutrient molecule. I know the ppms i have to stay above and under to maintain excellent growth because i paid attention to it for every single grow since i started.
That type of familiarity can be worked out in soil too, but depends a lot on the consistency of the soil you buy. more than one way to skin this cat.. pay attention, take notes.. adapt and improve continuously.