The Victoria and Albert Museum holds the golden throne of Maharaja Ranjit Singh Ji, made by Hafez Muhammad Multani, taken after the annexation. The Royal Collection holds Sikh material presented or taken. The British Library holds manuscripts and the India Office Records. The Wallace Collection, the National Army Museum and several regimental museums hold arms taken in 1846 and 1849.
The Koh-i-Noor is in the Tower of London.
The Toor Collection in London, assembled privately, is now among the most significant collections of Sikh material anywhere and has been exhibited and published.
Museums in Canada and the United States hold material from the diaspora communities and from private collectors including Narinder Singh Kapany, whose collection endowed Sikh galleries at several institutions.
The arguments about restitution apply here as elsewhere, and the practical position is that a Punjabi wanting to see the throne of the Sikh state has to go to London.
There is no consolidated catalogue of Sikh material in world collections, which would be a useful thing for somebody to make.
The Lahore treasury was taken in 1849 and its contents dispersed. Objects from it are at Windsor, in the Victoria and Albert Museum, in the Wallace Collection and in private hands.
Provenance for most of it is a line in an officer's will or an entry in a nineteenth century sale catalogue. Tracing an object back to a particular room in Lahore is possible for very few pieces.
Some of it is well displayed and catalogued, which is more than can be said for what remains in Punjab. That fact complicates every argument about restitution.