Constitutional practicability of referendum on EU Constitution

Yes. Binding referendum mandatory if constitutional amendment effected. Otherwise only evitable if not approved by a majority of 5/6 from members of parliament.

Approval of transfer of sovereignty without effect of constitutional amendment

Majority of 5/6 from members of parliament, § 20 ConstDenmark. If majority of 5/6 is not reached but a majority of votes and government holds on to the transfer of sovereignty, a referendum has to be called, § 20 ConstDenmark. Even if majority of 5/6 is reached a referendum can be called by a special law, § 42 I, VI ConstDenmark.

Approval of transfer of sovereignty with effect of constitutional amendment

Not expressly regulated but constitutional amendment required.

Approval of constitutional amendment

Majority from parliament after its disbandment and re-election, additionally by mandatory and binding referendum, § 88 ConstDenmark.

Other constitutional regulations about referendums

Referendum on laws can be called, § 42 ConstDenmark.