I recently converted to Islam and would like to take on an Islamic name. There are two that I really love Jennah and Sameeha. Can I use the two together Jennah Sameeha?

Yes, absolutely. It is common practice in some Muslim cultures for a woman to have two names. Jennah means Paradise and Sameeha means generous. You can consider the name Jennah Sameeha to be two separate good words, which is what I recommend, or you can consider their meanings together to mean "Generous Paradise", by making Sameeha and adjective of Jennah.