I accidentally cut an onion (don’t remember whether it was dairy or meat) with a meat knife on a dairy plastic cutting board. Then the onion was fried on a dairy pan and transferred to a dairy ceramic bowl.
The onion was subsequently discarded as I realized what happened. What do I do with the knife, the board, the pan and bowl?
The answer to your question really depends on whether the knife was really meaty and was used in a kli rishon (it was used to cut or stir hot meat in a pan or pot). If the knife was not used for such a type of hot meat, then in retrospect everything is fine because we will not say that the onion became actually meaty. However if the knife was used for hot meat at the level of a kli rishon, then the pan will need kashering. The type of kashering that it would need would depend on the amount of oil that was used. If it was only a minute amount of oil, then we say that the pan absorbed the meaty taste directly from the onions and it would need libun (burning it out). If however there was an amount of oil that it would be considered frying in the oil then hagalah (purging with hot water) would be needed.
Regarding the ceramic bowl, since it was only a kli sheini, and it can’t be kashered, we will be lenient that it doesn’t need to be kashered at all.
The cutting board is fine, because in retrospect we don’t say that he knife’s cutting on top of it makes it meaty.