[Alneyan]

You will get one level per inclusion of the technology in the trade. So, if you only have Destroyers, you will get Light Cruisers if you ask for one level of Ship Construction.

If you wanted to get enough levels to reach Dreadnoughts, you would have to add Ship Construction several times to your list (five levels if you already have Destroyers), assuming your trade partner has enough levels to give you.