According to many news outlets, most, but not every nation has agreed to the terms of the Paris agreement. Which didn't? Is there a public list of all signees?
Short answer: out of the total membership of the UNFCCC, ALL member countries either signed or registered accession ot the treaty*
Every country in the United Nations Framework Convention on Climate Change (UNFCCC) (195 countries in total), plus the institution of the EU (the 196th member) agreed to the terms of the Paris Agreement - the UNFCCC can only pass agreements without objection, there is no scope for a majority agreement. The Paris Agreement was agreed unanimously.
The register of signees is indeed public: the UNFCCC has a page dedicated to the status of its ratification. On the day that the register opened for signing, 174 countries, and the EU, signed. This was a new first-day record for an international treaty. 15 countries had also ratified it by that date.
There are countries that are not members of the UNFCCC. So whether they agree with the Paris Agreement or not was not recorded as part of COP21.
At the time of asking the question, no countries had yet signed the COP21 Paris Agreement, because it didn't open for signing until 22 April 2016, and will be open for signing for one year. From that link:
Following the adoption of the Paris Agreement by the COP (Conference of the Parties), it will be deposited at the UN in New York and be opened for one year for signature on 22 April 2016--Mother Earth Day.
The agreement will enter into force after 55 countries that account for at least 55% of global emissions have deposited their instruments of ratification.
The Paris Agreement met its entry criteria on 5 October 2016, and entered into force on 4 November 2016. By that time, the number of UNFCCC participants was 190 countries plus the EU. Five further countries signed after that , and on 21 September 2017, Nicaragua also announced it would sign (it had been holding out as it felt the Paris Accord was insufficient): it was too late for any country to sign by that date, as the window for signing had closed, but nevertheless, countries can still sign up to the treaty by lodging an article of acceptance, approval or acccession. Nicaragua lodged its article of accession, leaving only Syria as the only UNFCCC country not to. And then on 13 November 2017, Syria lodged its article of accession to the treaty too.
So out of the total membership of the UNFCCC, all member countries either signed or (Syria, Nicaragua) registered accession to the treaty.