I have no idea at all. But one thing I do know is that if you spread the blame too thin, everyone will get away with it! So be careful and identify the main culprit(s) only....
SDGs are universally accepted goals. All countries, societies, NGOs, scholars, institutions, etc. have a responsibility to ensure the attainment of the noble goals it sets out.
Though there may be specific institutions mandated to ensure effective implementation, all are each others keeper in ensuring that the goals are attained across board. Thus, everyone becomes a watchman over their neighbor.
I have been lucky to direct my institution's Semester on the United Nations for the last 10 years or so. And my students and I have participated in meetings were the SDGs have been the focus of the conversation. Several years ago when the SDGs were being drafted we attended many meetings in the UN HQ that asked whether these goals were achievable. If so, your question of accountability is correct. But, most people in the room - from the NGO community, UN Secretariat staff and some diplomats - knew that the SDGs are very ambitions and it would take a lot of money to actually make the happen. I have seen reports that the international community would have to dedicate anywhere between $1 to $3 trillion to fulfill the goals. This is of course is not going to happen.
The SDGs build on the Millennium Development Goals (MDGs) experiment. These goals were pretty much decided by the UN Secretariat with donor member-states (read richest countries in the world) to re-energize development and to try to reduce extreme poverty (defined as people who live with less than $1.90 per day) by half. The MDGs were not fully met, but progress in the 8 goals were made. Yes, extreme poverty was reduced by half, but the progress took place mostly in India and China, where high economic growth improved living standards. Data from subsaharan Africa, Latin America and so forth were not as positive.
The SDGs were adopted after the UN Secretariat hosted a series of meetings - for close to a year - with civil society, all UN members, the World Bank, IMF, and other donors. It was extensive process. And while we can debate whether 17 goals are better than 8 or whether there are too many subgoals, the international community has embraced these objectives, the UN has put in place mechanisms to measure compliance with these goals, and the family of UN organs, subsidiary bodies, specialized funds and agencies are trying to mobilize resources to fulfill these goals.
Not all countries will be able to meet these goals, but if most due then humanity will be better off.
Another point that is worth noting is that the 8 MDGs were mostly meant for low-income and middle-income countries. The high-income countries were supposed to support the process financially, with technical assistance and so forth. In contrast, the SDGs as conceived due require high-income members to make progress in different areas such as climate change, clean water, food safety, etc...
In reality all UN members are accountable in terms of their commitments to fulfill the 17 goals. And the UN through is different data collection and analysis mechanisms points out areas where members have to do more. And the UN can work with the IMF, World Bank and other donors to target funding to help members achieve the goals. This is a complex processes with many stakeholders. Thus, accountability is spread so thinly that no person, state or organization will be responsible for either the success or failure of the SDGs in 2030.