I have bought a (roughly five litre volume) electric rice cooker that looks like this:  Notice the small hole at the top lid, that I suppose is for letting out steam. During cooking, is it ever needed to put a dry cloth to cover the hole? And, if I do put a dry cloth while it's in cooking mode (or warming mode), are there any risks? (for example, my food will be burnt) I am mostly using this electric rice cooker to cook rice, oats, boiled vegetable, pulses, etc. The idea to put a dry cloth covering the hole comes from my mom who has been using old pressure cookers for years (like this one). 
Very simple: don't cover it at all, ever. There is a reason for the hole being there. It is there to let stuff out! Usually clean steam, but if you loaded the cooker wrong, a bit of mess can come out. Then you should be happy that 1) it is coming out and not interfering with the cooking process inside, and 2) drawing your attention to the fact that you have loaded it wrong, so you know better next time. Just clean the mess. In a pressure cooker, it is doubly important to not cover it! It is there as a safety mechanism, to prevent an explosion. Yes, I mean a real explosion, which will damage not just the pressure cooker, but also a good part of your kitchen! While pressure cookers made for home use are very safe, this depends on them being used as intended, and especially on not obstructing their safety valve in any way. If you want a cleaner kitchen, simply position the rice cooker in a place where its steam hits something wipable, like a tiled wall. You can also put some kind of easy-washable foil on the underside of your upper cabinets above the cooker, or attach some multi-layer paper (an old magazine will do) which you then exchange regularly. But you have to live with the fact that you will have steam (with slightly dirty aerosol) coming out of that hole, that's what it is for. 