Complex sentence: When he remembers that a tattoo was put on the upper part of his elbow joint; but when suddenly he removes a bandage covering the same area, he finds no tattoo; this gives us a hint that he was actually in a dream.
Split into simpler sentences: When he remembers that a tattoo was put on the upper part of his elbow joint; but when suddenly he removes a bandage covering the same area, he finds no tattoo. Which gives us a hint that he was actually in a dream.