Dryers are light and you should easily be able to pull it out from the wall so you can have a look at it. Whilst both electric and gas dryers require electricity to operate, gas dryers also require a professionally-installed gas hook-up from your gas supply. This will be quite recognisable, and of course there will always be a gas shut-off valve, which will be easy to reach. The shut-off valve should be turned to the ‘off’ position before moving it out from the wall completely, as the gas supply pipe may become disconnected. Gas pipes are often easily identifiable and usually yellow in colour.
Also, if it is an electric dryer, the power input will be larger than what a normal household electricity socket provides, so the wall socket will almost definitely be larger than usual. The power supply should 220V.
If you do not have access to the back of your dryer for whatever reason, a good idea would be to note the model number and brand of your dryer and contact the manufacturer for guidance. The big white good manufacturers will definitely have a hotline, often on a ‘0800’ number, which you will be able to ring in order to speak to someone who knows exactly what powers your particular dryer.
This would be a good idea too if you are worried about disconnecting any gas pipes by pulling it out. There is no better solution than phoning the company up to receive sound and professional advice.