Can anyone tell me any exclusive application of Johnson counter?

If you attach suitably-valued resistors to the outputs of a Johnson counter, you can synthesize some very high-quality sinewaves.

Here is one example of this.

If you are making a decimal counter and decoding it, a Johnson counter uses 5 rather than four flip-flops, but can be decoded to 10 outputs with only 2-input gates for a net saving in CMOS technology.

Below is an example from the CD4017 datasheet.