What would you do?

Assume you saw this on your plant.. what would you do to troubleshoot and fix the problem. I think I already know what is going on I'm just curious to see how other people approach problems on their plants.

Id check the heat, lights too close or it needs repotting.

if not the lights creating to much heat or being to close than I'd say an iron defficiency

First I'd need to know how it's being grown, nutes used, and ambient conditions. But first I always check for bugs, which I don't think is your problem. Then I move on to other areas, but without having any knowledge of your conditions, I have no clue... Does look a little dark on the green, could be the start of a (P) def. Are your stems purple? Could also be the start of a PH issue.
That's about all I got for now...
GS

I had someting similar on my plants and it was from the lights being too close. I would check lights first, then look for bugs and keep track of the nutrient feeding. Bugs would be the last thing I suspect but i would check early just in case because the sooner you catch them the easier it is to deal with