which is

[navi tasan]

Can one say in informal English:

1-He says he is a cardiologist, which is I don't know what. (...but I don't know what a cardiologist is.)

2-He says he is going to meet the famous Jane Hopkins, who is I don't know who. (...but I don't know who the famous Jane Hopkins is.)

3-He says he is in Lory, California, which is I don't know where.

[Barb_D]

I wouldn't. You may hear something like this:

... in Modesto, which is [pause, when you realize you don't know] I don't know where.

But you wouldn't say it as a continuous utterance.

1-He says he is a cardiologist, but I don't know what that is

2-He says he is going to meet the famous Jane Hopkins, whoever that is.

3-He says he is in Lory, California, but I have no idea where that is.