I've been repairing electronics for over 40 years, dry joints are caused mainly by poor design and by poor quality construction - if you properly hand soldered the joints in the first place, they would probably never fail.
As JimB has already pointed out, the normal places are on larger components, such as transformers, large transistors on heat sinks, large capacitors, metal earthing strips across the board etc.
All these tend to 'suck' the heat away during flow soldering, and I suspect they tend not to get soldered very well because of this - normally cleaning the joint and hand soldering means it never reoccurs. Other problems are mechanical stress, again with heavy components where the only mounting is the solder joints, and also components subject to high frequency vibration such as transformers and inductors in LOPT stages or SMPSU's.
There was a classic example on an old Bush CTV (BC6100 series - late 70's/early 80's?), these commonly developed dry joints on a pincushion transformer - Bush solved the problem by hand soldering the transformer connections after the board had been flow soldered, and by using high melting point solder (which has greater mechanical strength).