#Java 8, 56 55 bytes

v->" s\n uns\nun s\nun uns".replaceAll(" |s","known$0")

-1 byte thanks to @SuperChafouin.

Explanation:

Try it here.

v->                         // Method with empty unused parameter
  " s\n uns\nun s\nun uns"  //  Literal String
   .replaceAll(" |s",       //  Replace all spaces and "s" with:
     "known                 //   Literal "known"
           $0")             //   + the match (the space or "s")
                            // End of method (implicit / single-line return-statement)

Java 8, 56 55 bytes

v->" s\n uns\nun s\nun uns".replaceAll(" |s","known$0")

-1 byte thanks to @SuperChafouin.

Explanation:

Try it here.

v->                         // Method with empty unused parameter
  " s\n uns\nun s\nun uns"  //  Literal String
   .replaceAll(" |s",       //  Replace all spaces and "s" with:
     "known                 //   Literal "known"
           $0")             //   + the match (the space or "s")
                            // End of method (implicit / single-line return-statement)

#Java 8, 56 bytes

v->"x xs\nx unxs\nunx xs\nunx unxs".replace("x","known")

Try it here.

#Java 8, 56 55 bytes

v->" s\n uns\nun s\nun uns".replaceAll(" |s","known$0")

-1 byte thanks to @SuperChafouin.

Explanation:

Try it here.

v->                         // Method with empty unused parameter
  " s\n uns\nun s\nun uns"  //  Literal String
   .replaceAll(" |s",       //  Replace all spaces and "s" with:
     "known                 //   Literal "known"
           $0")             //   + the match (the space or "s")
                            // End of method (implicit / single-line return-statement)

#Java 8, 56 bytes

v->"x xs\rx unxs\nunx xs\nunx unxs".replace("x","known")

Try it here.

#Java 8, 56 bytes

v->"x xs\nx unxs\nunx xs\nunx unxs".replace("x","known")

Try it here.