A link to the other thread:http://www.slaegtogdata.dk/forum/index.php/topic,34338.0.html
Hi Seidi, maybe you can say a little more to help those who do not read Danish (as the other thread is in Danish).
This may not be necessary - someone may find him anyway. But John Jensen is a common name and so additional identifiers might help in distinguishing him from the crowd.
My quick search of ddd.dda.dk emigration database and Ellis Island did not find him, so helpers will turn to Ancestry.com to help you.
I admit I am curious why you currently know he immigrated to USA on the Red Star Line in 1927, yet you ask for help finding his immigration?
Typically useful identifiers:
The full place name where he is from -
Last known residence before 1927 immigration -
Parents and siblings names, who may have also immigrated, thus could be clues in identifying him in USA - or they may be named on a ship's manifest as persons to whom he is traveling or with whom he had last contact in Denmark
Possible destination in USA