What kind of blood are you looking for if it’s burst’s probably go with Andrew Kramer or Denotation Films. But if your going for the look of a knife stabing in someone or a slice mark you could make a red solid and draw a mask around the place you want the blood and apply effect>Distort>Turbulant displace, and change the amount to around 30 the size about 15 and the complexity to 5 and you can adjust it from there. Know for the red solid layer change the transfer mode to classic color burn and it will have the effect of it blending with the shirt. if your working with the professional version you can track the knife and create a null object and put the track target to the null object and parent the red solid to the null object and it will move with the body. If you don’t know what parenting is it is the little coil looking thing by the transfer modes, and just click and drag it to the null object and that will parent it. If you don’t see the transfer modes or the parenting whip hit F4 to toggle the different option