Note, dbo.DelimitedSplit8K is the fastest way to split sting in T-SQL (it only will marginally loose to CLR implementation). Also, what will happen if your Category will include 3 or more skills: HTML/ASP.NET/C#?

You will need to amend Alan's solution in order to deal with this (making it slower). Using DelimitedSplit8K splitter, you don't need to worry about this and scalability.

Try to make it working. I guess you have some other object in your database called Category. Try to put table alias at front of Category inside of function:

select d.Item as [Category], COUNT(*) AS Count

from @mytable t

cross apply dbo.fnSplit(t.[Category], '/') d

group by d.Item