The Lord appeared and stood by Paul. This is the second time, once as a light on the road to Damascus, now bedside in Jerusalem. Note that Jesus did not appear to everyone there at the time of the testimony and riot in Paul's defense, Paul was there to appear in Jesus' defense and after word Jesus appeared in His own time to comfort Paul. This is an important distinction to grasp. Why Jesus does what He does and doesn't do what He doesn't is His masterful judgment to make and as His servants ours' to live within.
How Paul's nephew found out about the Jewish assignation plot we are not told. Being at the right place at the right time I suppose. It could be that someone from within the Jew's confidence sought him out as well; which makes the account all the more interesting.
2012 - pBiblx2 Field Wise Bible System Version 2.0.9d - GPL3