Remove both Special Characters and String Characters from output SQL Server
Try this code that uses a combination of SUBSTRING, PATINDEX, LEN, and REVERSE, to account for the possibility of 10-13 digit ISBN variability to return the exact ISBN with no trailing extras:

declare @myvar varchar(50)='C9781501132957 : (hardcover)'
SELECT substring(@myvar,2,LEN(@myvar)-   PATINDEX('%[0-9]%',reverse(@myvar)))


...or perhaps differentiating between other numbers in the string from ones that are at least 10 digits in size, like maybe a date of 1987 included in the description (if this is even needed):

declare @myvar varchar(50)='C9781501132957 : (hardcover) 1987'    
SELECT substring(@myvar,2,LEN(@myvar)-   PATINDEX('%[0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9]%',reverse(@myvar)))


i.e.

Select DISTINCT t.processed 'Title',
substring((Select max(reconst) from isbn where bib# = t.bib#),2,LEN(@myvar)-   PATINDEX('%[0-9]%',reverse(@myvar))) 'ISBN',    t.bib# 'Bib#',
(select max(collection) from item where bib#=t.bib#) 'Collection',
convert ( varchar(3), (Select count (*) from item i where i.bib# = t.bib#)) 'Total Items',
(Select count (*) from item i where i.bib# = t.bib# and item_status not in ('o','l','cr','m')) 'Eligible Items',
(Select count(*) from request r where r.bib# = t.bib#) 'Requests'
from title t
inner join isbn
on t.bib#=isbn.bib#
inner join item
on t.bib#=item.bib#
where t.bib# in (Select bib# from request)
and convert( int, (Select count(*) from item i where i.bib# = t.bib#)) &lt;
convert( int, (Select count(*) from request r where r.bib# = t.bib#))
order by Requests desc