Regardless my political standing, an endorsement is an endorsement. If Trump wants to be considered a serious candidate - by his own party, he will require endorsements to do so. Paul Ryan is influential, and his endorsement will surely mean a lot to people that do believe he is an outstanding person. It will only benefit Trump if he is elected that he has someone in the House of Representatives.
Donald Trump is not going to win the election unless he gains support of major republican leaders. His supporters are mostly extremists, and there are not likely to be enough extremists for him to win the election. Paul Ryan is one of the best known republican leaders today and his support would be substantial.
Donald Trump is floundering at this point. What he needs to do is to take a step back, step down from his high horse for a moment and see that he needs Ryan's help. He could learn SO MUCH from Paul Ryan, and all he has to do is forgo his ways and ask for help.
I am not a r\Republican and have not followed the elections that closely. However, if Trump feels that Ryan will help him with the polls and as president later on, I do not see why he shouldn't court Ryan's endorsement. Trump does whatever he does and I have no baring on his decisions in any way.