Single quotes within single quotes may be causing issues. Try this instead:

select *

from openquery([connection], '

-- Forum Messages by User

use databasebname;

select u.name, convert_tz(from_unixtime(m.modificationDate/1000),''+00:00'',''-08:00'') as TimePST, m.subject, m.body, m.messageID, f.forumID, f.name

from jiveMessage m inner join

jiveUser u on m.userID = u.userID inner join

jiveForum f on m.forumID = f.forumID

where from_unixtime(m.modificationDate/1000) > date_sub(now(), interval 1 week)

and u.name like ''Luke''

order by m.modificationDate desc ')