Search Siri Guru Granth Sahib ji for Ang 1106. You will find something that looks suspiciously like a yoga kriya given by Yogi Bhajan, as you call him. Yes, Guru ji says to inhale through one nostril, hold the breath and exhale through the other nostril as a way to focus the mind. Meditations to help focus the mind are sometimes helpful because if we just recite bani while the mind roams all over, we are not truly doing bani.
As far as focusing on the nose, apparently it is recorded in history that Guru Gobind Singh gave this instruction to his wife, Mata Jeeto ji. Using this method and dedicating herself to this practice she attained a great meditation and perceived the future.
"Gur mantra dey mata ko, boley sahib nal piara. Drisht taravo nasika basai Amrit dhar."
"Guru ji gave the mantra to Mata ji and he spoke to her with love, 'Put your focus on your nose, and amrit will rain down on you.' "
There is a version of this history in the Siri Guru Pad Prem Prakash by Baba Sumer Singh where it is also recorded that Guru ji instructed her to look at the nose.
This is a way of focusing the mind which will then be ready for a more powerful meditation. Focusing on anything can help tether the mind under control. Focusing on the nose is an excellent method because when you are looking at it, you know exactly when you are losing focus. Where if you focus on something while your eyes are closed it is easier to forget that the focus has been lost.
These are ancient practices, the likes of which were much more common in Sikh culture before the time of the British.