Possible meanings are 1) "he says meaningless things" or 2) his enemies say things to make him think that they are his friends when they are not. Alternate translation: "he says deceitful things" or "they pretend to be concerned about me" (See: [[rc://en/ta/man/jit/figs-idiom]])
His enemies try to learn all of the bad things about him. Here the word "heart" refers the whole person. The writer's sin is spoken of as if it were an object that could be gathered. Alternate translation: "he tries to learn about all of my sins" (See: [[rc://en/ta/man/jit/figs-synecdoche]] and [[rc://en/ta/man/jit/figs-metaphor]])