Group By column on SQL Server and concat inner join to that grouped column

Without sample data it is hard to tryout, but maybe this can help you

First I create some sample data, but I have no idea if this is correct with your data

declare @Lista table (Id int, Nombre varchar(50))
declare @ListaDetalle table (IdLista int, Valor varchar(10))

insert into @Lista (Id, Nombre) values (1, 'Lista clasfication'), (1, 'Lista clasfication'), (1, 'Lista clasfication'), (7, 'Lista final'), (7, 'Lista final')
insert into @ListaDetalle (IdLista, Valor) values (1, 'a'), (1, 'b'), (1, 'c'), (7, 'Valor 01'), (7, 'Valor 02')

Now we can use this query which returns what you asked in your question

select l.Nombre + ': ' +
       ( select string_agg(ld2.Valor, ',')
         from   @ListaDetalle ld2
         where  ld2.IdLista = l.Id
       ) as Nombre 
from   @Lista l
  inner join @ListaDetalle ld on l.Id = ld.IdLista
group by l.Id, l.Nombre

The result is

Lista clasfication: a,b,c
Lista final: Valor 01,Valor 02