I cut an onion with a pareve knife and immediately afterward I cut a cold piece of meat.(there were still traces of onion on the knife) Did the knife become fleishig?(Do we apply davar charif and duchka d’sakina here?)
The knife remains parev, and does not become meaty.
The general principle of davar charif applies when a sharp item (such as an onion) is cut with a knife, thereby combining the pressure of the knife with the sharpness of the food. However, the presence of a sharp sauce will not cause the knife to absorb the taste of the meat.
See Shulchan Aruch, Yoreh De’ah 96:1 and commentaries. Since there is no dochka against the sharp item, the prinicple will not apply to the case of the question.
Sorry about the delay in answering this question.