Sceat research does not take place in the Research Tower like other researches, but in the Hall of Legends under Sovereign buildings and Sovereign units tabs. To start researching at all, you need to reach level 70/650 and have some sceats saved up.
Each tab contains two separate chapters of research.
Most sceat researches (not all) need to be done sequentially. For example, research the building, build it, and only then can be unlocked the research of the next building. You can see this in the research conditions for that building/unit/tool. In the case of units, you must first research all levels of units on the first line of research to start researching the second line. The same goes for tools. You always need to fully research the entire research line before you can start the next one.
All researches are also limited by levels. You can see this in the tables below.
Sovereign skills – buildings I
Sovereign skills – buildings II
Sovereign skills – units
Sovereign skills – tools
Here you can see how many rubies it would cost you to skip researches. Author: @Cooldog
Can I run multiple researches simultaneously?
Yes, but only from different tabs. So you can run one research in the Sovereign buildings tab and another research in the Sovereign units tab. For example, you cannot research units and new tools simultaneously.