Is this old caulk at the trim on the edge where roof meets the sidewall?
If you need to fix this immediately, try removing the screws that hold on the trim piece. If you can, get some gray butyl caulk tape at a local RV or trailer supply. If you can't, pick up some Dicor or C-10 self-leveling sealant at your local big-box hardware place. If you can't find that, any good elastomeric caulk.
NO SILICONE. Repeat, no silicone.
Remove any loose caulk. Apply the new caulk all over in the roof area under the trim piece, including all the screw holes. Replace the trim and screw down with all new screws, preferably stainless screws.
If there is any place the screws won't bite, try a longer or thicker screw at that point, or at worst, fill the hole with caulk so it is not a leak source.
Later you can order some Eternabond tape and apply over the trim to permanently seal this area (see the multiple threads about Eternabond).
Many RV owners have tried the "squirt in a little caulk where you see a hole" type of repair, and it rarely repairs.
As always, JMHO