Can I use the same adaptor plug in Germany, Italy and Spain? Or do I need 3 different ones for my ha

Sure you can. No need any adapter.

Can I use the same adaptor plug in Germany, Italy and Spain? Or do I need 3 different ones for my hair dryer?

All of Europe uses the same plug, so you only need the one adaptor. The only different one is the UK.

Can I use the same adaptor plug in Germany, Italy and Spain? Or do I need 3 different ones for my hair dryer?

I believe they are pretty similar. Many countries have the same two prong system, but the third grounding plug varies from country to country. We lived in France, and everything we bought there generally worked in Germany, Italy, and Spain.

Can I use the same adaptor plug in Germany, Italy and Spain? Or do I need 3 different ones for my hair dryer?

Should be no problem using the same one...