Black spots in the kitchen sink

If you zoom in and take a look at some of the striation marks running through the suspect stuff:

... you can see that something was able to scratch through it easily, probably flatware or a knife. I personally use the same chainmail scrubbers that I use on cast iron to clean that sort of stuff off of stainless. It won't leave 'tracks' like steel wool / Brillo might.

Whether or not it's mold would be up to a field test to confirm, but I highly suspect it's just some muck / soot from a pan, you generally don't see mold settle in sinks outside of ring seals around them or the drain.

Some hot water and a good scrubbing should be all you need.

Use a journal to document when and how ofter you have to clean this? Consider: Professional kitchens/hospitals have constant moisture and running water in their stainless steel sinks and DO NOT have black mold build up every three days or so after cleaning with bleach? If you rent your flat why on earth do you have to incur the expense of bleaching every day? the water should be safe. If you "clean" your sink and every couple of days this persists 1. take pictures and share with your landlord in writing a detail of your issue(s). 2. Call a plumber/mold expert share your story. 3. have a professional )not the "maintenance man" come out and take a look. 4. Contact your doctor and ask him/her how mold can affect your health. Remember there are MILLIONS of people who do NOT have any black splotches recurring on their stainless steel sink and whose water does not spew this mold. Take off the aerator ( they are cheap like $2.00) and clean it in fact leave it off for a couple of days and see if the "mold looking stuff" returns. If it does you may have a mold issue in your plumbing and that your landlord must address:). Take care and good luck. Do't believe yourlandlord believe your gut!