I wish I had known when he came.



Ei wisch ju watt! ;-)))

That doesn't sound quite right. Try:

I wish I had known when he was going to arrive (…then I could have picked him up)

Baxter's suggestion is probably best, if that is what you want to say.

The two sentences (1) and (2) have different meanings. They would both be possible in different contexts.

I'm not sure what you mean by
'It comes from " I wish I knew when he comes." '
In correct English, this would mean ". . . when he habitually arrives", e.g. "I wish I knew when the postman (usually) comes."

If you want to express a wish relating to your present knowledge of the future, you might say "I wish I knew when he will come". ("If I did, I could have a meal ready.")

I would analyze " I wish I had known when he would come" as follows:

Statement or belief "I know when he will come."

If you now wish that you could have made that statement in the past, you could say:
"I wish I had known when he would come."
("I could have put the wine in the fridge exactly two hours before.")

"I wish I had known when he came" would be grammatical possible in two senses:

1) I wish I had known (in the history test) when he (Columbus) came (to America).

2) I wish I had known (that he was a serial killer) when he came (and I invited him to come in).