I'm not sure how often.. I just find one here and there around. I wouldn't really worry about finding two, unless you start finding more, or notice the kitty's whiskers getting sparse.
My cat lost no whiskers (that I noticed) for the first 10-12 months of his life, then one week I found about 6. I was at my vets anyway the week after, so I asked her and she said unless a cat loses ALL his/her whiskers, its nothing. Since my cat dropped so many whiskers, he's had all new ones grow back. I wouldnt worry about 2 at all
Thank you both for alleviating my fears. This is the first time I've seen whiskers shed, so it did give me some concern. I wish Cairo would shed her 2 black whiskers. She is orange everywhere, and out of each side is 1 black whisker. She also has a black patch under her tongue. I have no idea why black came out. It would make more sense on Paris who has some black in her.
Oliver loses whiskers occasionally too... he's all orange and sometimes his whiskers grow back black, haha... he's got a couple black ones right now.... for some reason (I think it's still unknown why exactly) orange kitties can have black spots appear on their noses and inside their mouths... Ollie has like 2 tiny black dots on his pink button nose and I always catch myself trying to brush them off hahaha - I'd think the black whisker thing happens for the same reason - whatever that is haha
The orange kitty at work has about 50/50 black and white whiskers... and my sister's kitty varies from mostly white to mostly black to various in between points.. it's kind of amusing.