As presented your string appears to have no multiple spaces, but to have spaces at the start and end. To solve the problem you asked, I would use a Java Snippet node configured to replace your incoming column:
String str = c_MyColumnReferenceHere.trim(); //Incoming column
while (str.contains(" ")){ //2 spaces
str = str.replace(" ", " "); //(2 spaces, 1 space)
}
c_resultColumn = str; //Result column
Steve