Any idea why are all my coffee leaves brown at the tip?
brown tipped coffee leaf
Hard to tell but the first thing that comes to mind is inconsistant watering. How large is the pot and how large is the plant? Sometimes if a plant has been in a pot for too long it is all roots and no soil to hold moisture. It may just need to be re-potted but that is only a guess at this point.
Could also be buildup of salts in the soil from fertilizer, hard water, etc. To minimize that, make sure when you do water that you water thoroughly (vs in little sips) since this will help flush out salts. And you'll need to repot from time to time into fresh soil even if the plant hasn't outgrown the pot that it's in.
Tip burn like that can also be caused by a sudden dose of fertilizer. If you put in some granular fert, then had a heavy rain it can give a potted plant a big dose all at once that can burn the leaf tips. Using a coated, timed-release fertilizer helps prevent this happening.
Again, repotting will help solve this problem. Beware that some potting soil has fertilizer added, though.