How high does sorcerer skill get?
Unlike with wizards, I'll assume as a base that the sorcerer is a dark elf rather than a race with neutral stat bonuses. Statistically, players have made this true due in some part to a combination of Faendryl lore and the calculations for sorcerer CS using Aura and Wisdom, which dark elves have the best bonuses in. As for ensorcelling, that uses Wisdom and Intuition, which leaves dark elves and halflings tied for the best.
642 is achievable without using Ascension nor enhancives on a dark elf (or halfling) using a fairly typical post-cap build with 170 ranks of Sorcerer Base and all other relevant ensorcelling skills maxed out through ordinary training.
652 is the same as the above, but with the use of BOOST ENHANCIVE STATS from daily logins.
730 is the same as the above, but now also wearing an incredible enhancive set to finish maxing out Intuition and Wisdom in addition to maxing out Magic Item Use, Arcane Symbols, Elemental Mana Control, and Spiritual Mana Control. (Finding someone with such an enhancive set is very unlikely!)
775 is achievable without using Ascension nor enhancives on a dark elf (or halfling) using a mutant build with 303 ranks of Sorcerer Base and all other relevant ensorcelling skills maxed out through ordinary training.
785 is the same as the above, but with BOOST ENHANCIVE STATS.
863 is the same as the above, but now with the full set of enhancives.
913 is the same as the above, but now with the extremely expensive +50 spell rank enhancives from the High End Scrip Shop.
1000 is the same as the above, but now also the astonishingly time-consuming 1400 Ascension Training Points to nearly max out every skill. (Magic Item Use, Arcane Symbols, and one out of Elemental or Spiritual Mana Control can stop two ranks short of maxing.)
In summary, 1000 is as high as theoretically possible, but a range of 642 to 710 is what you could more likely expect from ordinary post-cap sorcerer builds while 775 to 843 is what you could more likely expect from post-cap mutant sorcerer builds.