Here is one way of doing it:

select 'alter index [' + si.name + '] on [' + schema_name(so.schema_id) + '].[' + so.name + '] rebuild with (online = on)'

from sys.indexes si inner join sys.objects so on si.object_id = so.object_id

where si.object_id = object_id('TableName')

Adi