Six years ago, we bought a parking space with my friend. He paid 40% of the amount and I paid 60%. We are reselling it today for 27,000 euros. The notary tells me that I will be the only one to be taxed on the capital gain which is realized (...)

...  Is this normal? 

Yes. If in principle the capital gains made on the sale of real estate are taxed, there are exceptions, in particular when the sale price is less than 15,000 euros (art. 150 U, 6° CGI). If this property is held in joint ownership, this threshold is assessed with regard to each undivided share. Therefore, the sale price of your property being 27,000 euros, your friend's share is 10,800 euros (he is therefore exempt from capital gains tax) and yours is 16,200 euros (you are therefore liable for a capital gains tax).