My brother cut his non-halal steak hard and his knife slammed the plate. I saw a wet stain with black specks (like pepper) on my shirt, similar to what was on his plate. I'm worried juice/fat splashed on me. Would this fall under shakk or most probable that my shirt considered najis?

Ustadh AbdulAziz al-Haqqan

Clothes are pure by default and are only judged impure with certainty. So, if you were not certain, don't dig too deep as I am afraid that you suffer from waswas thus you are asking.