In a report published today, the Law Society of Scotland also questions Scottish Government plans to continue charging tuition fees to students from the rest of the UK following a Yes vote, in an apparent breach of EU law.
Challenging the main pro-UK parties, the Law Society urges Labour, the Tories and the Liberal Democrats to provide clarity on further devolution for Holyrood if Scots vote No in September's referendum.
The study calls on the three parties to explain how their "diametrically opposed" proposals for new tax and other powers would be reconciled.
The report, Scotland's Constitutional Future 2, says on legal issues the Scottish Government should set out transitional arrangements for cases already before the UK Supreme Court if, as the SNP plans, the body is replaced by a Scottish Supreme Court.
The study raises questions about pensions provision and warns the creation of a new tax system "could take years to achieve".
Alistair Morris, president of the Law Society of Scotland, said: "Despite much debate, a major White Paper, devolution commission reports, analysis papers and a draft Independence Bill, many of us believe important questions on Scotland's future remain unanswered.
"There continues to be uncertainty on fundamental issues including the currency we would use, EU membership, how our economy would succeed and what taxes we would pay.
"There are also questions over how further devolution can and would be delivered in the event of a No vote."
Lawyers representing both sides of the campaign clashed over the conclusions. QC and former LibDem leader Sir Menzies Campbell said: "With less than 70 days to go ... the pressure is really on the Yes campaign to spell out their plans on currency and the EU."
Speaking on behalf of the pro-UK group Lawyers Together, Patrick Layden QC said: "The process of actually separating Scotland from the UK will not be quick or smooth. It would take more than 18 months to negotiate with the rest of the UK on the terms of independence. We could not sensibly approach the EU until after we had done all that."
But Joanna Cherry QC, from Lawyers for Yes, said the Scottish Government had provided "considerable detail" and accused UK ministers of refusing "to engage in any meaningful contingency planning".
A Scottish Government spokeswoman said: "We have put forward our guide to independence in Scotland's Future, the most comprehensive and detailed blueprint of its kind ever published.
"An independent Scotland will keep the pound and remain in the EU as an independent member state. The only threat to Scotland's place in Europe, and the investment and jobs it supports, comes from Westminster's proposed in-out referendum - and the biggest cause of any uncertainty ahead of September's referendum is the UK Government's refusal to enter discussions on key issues."