I have booked 2 weeks in Lisbon Portugal and a week in Paris. I will be travelling with my 15yr daughter. Any advice on must see and do ? Renting a car in Lisbon etc. Thank you!

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Please don't stay the full two weeks in Lisbon!
Drive up the coast, stopping along the way (Sintra, Nazaré etc) and stay a few days in Porto.

Highly recommend the Home Lisbon Hostel!

It kindof depends on what you and your daughter like. I just did 3 days in Paris in May (and then 10 day road trip through Champagne region and Loire valley). I'm big on history and art, so a lot of museums were on my list. The Louvre is amazing, and amazingly massive. I spent 6 hours in there and probably only saw 1/3. Tip: Wednesday and Friday they are open late till 9:30pm. If you go, make a plan on what areas you want to see before you go. Its a bit of a maze of galleries and overwhelming. A little planning pays off big. I also did the Rodin Musuem, Notre Dame, Saint Chappelle, Pantheon, Cluny Medieval Musuem, d'Orsay Art Museum, and Arc de Triomphe (you can go on top of it for a great view of the city). I also saw the Eiffel all lit up at night, but didn't go up. There where many people there in the park Sunday night with blankets, cheese, and wine enjoying the evening. I also saw the Army Musuem, but unless you're really into it or want to see Napoleons tomb, I might take a miss.
Also take a trip to Versailles, but again be warned it is a huge estate. It's an all day thing. You can buy tickets in advance online before you go, but be prepared to line up to get in regardless. But it is worth it! Also learn from my mistake and bring sunscreen! I did notice bus tour groups seemed to get in quicker through another entrance. And personally I would avoid the fountain show days. I think Saturday. It's just crazy crowded, and imho not that spectacular. It's not timed to music, they just play music while they turn the fountains on. Meh. Fontainebleu is also another royal palace outside of Paris that I definitely think is worth seeing. Perhaps even more ornate than Versailles inside, but lacks the huge park grounds. I think there is a train to/from that takes about an hour.
Also a bit of research on transit is good. I was lax on this. Despite it being a huge, cosmopolitan city, I was surprised that buses and the Metro didn't run late into the night. And be a bit wary of taxis. I took a couple good trips with them, but a 3rd driver tried to rip me off big time after a show with a flat rate back to my hotel. He asked 40 euro (I got wary when he said his credit card machine was broken, and cash only), and the taxi I eventually caught only charged about 12 euro on the meter. Uber is also an option. I also found the city very walkable, and was staying in the Latin Quarter near the Sorbonne which is somewhat central to many attractions.
One recommendation I would have is the Paris Museum Pass. Pays for itself if your doing a couple of the musuems/attractions. AND it gives you priority access to many of them, which is worth it's weight in gold. Some of the ticket and security lines are long. There is also a City Pass, but from what I could tell it didn't offer much more I was interested in and was 3x the cost.
http://en.parismuseumpass.com/

If you rent a car in Portugal, don't drive in Lisbon, it is just too chaotic - save the driving for outside the city - check out this blogger, she lives in Porto, but has lots of info for all of Portugal - https://gailatlarge.com/blog/ Also check out http://www.spottedbylocals.com/ for Paris and Lisbon, lots of local (less touristy) things to see and do which gives a much truer feel of the cities - tourist hoards can be overwhelming, try and see major locations early or late - the tour bus crowds start appearing about 10AM and are usually done by 4PM

Caiscais

A road trip north from Lisbon...Obidos, Alcobaca, Fatima, Batalha are nice cultural sites. The beaches of the Costa Prata are lovely and you might even consider driving into Northwest Spain to see Santiago de Compostella and / or La Coruna.

I highly recommend a free walking tour in Lisbon. They are really free, and ask for a tip at the end and they are so incredibly knowledgeable. We had so much fun! Check out Airbnb's for accommodation - we stayed in a beautiful apartment right in the heart of the Alfama district and it was perfect!

Thank you very much!

You do not need a car until you leave Lisbon. Sintra is a must see and you should schedule two days for that. Porto is lovely and is worth a 4-5 day visit itself.

And yes to the walking tours

Obidios! Cape St Vincent, Cascais, Evora, Sinatra, a boat tour from Portimao to see cliffs and caves.