Big thumbs up to what dapet just said! Insight genesis is awesome and I've just started using it, I'm still learning but u should pick it up quick.....
In the insight genesis program online you can look at the map it made of your sonar log and see the replay of either your 2d sonar or down image....... You can also mark waypoints but I've not figured it out yet, you can't mark on the sonar log just on the map so that doesn't seem very accurate and I'm not sure how to get those waypoints to your map ( someone set me straight if I'm wrong)
They say there is a sonar viewer u can download from web but I can't find one that'll play my logs, wrong file type