Questions here

1. where postcode = 'KA%'
   This will search for postcodes which contain the 3 characters KA% - and will match no records. You need to state:-
   where postcode like 'KA%'

2. where postcode like 'KA*'
   This will not match any records, as the wrong wildcard character (*) has been used.
   You need to state:-
   where postcode like 'KA%'

3. where last_donation_date like '01-Sep-%
   You cannot use on a date a wildcard which is for string searches.

4. where title = ('MISS','MRS','MS', 'Ms', 'Miss','Mrs')
   A title cannot equal all of these different values. You need in:-
   where title in ('MISS','MRS','MS', 'Ms', 'Miss','Mrs')

5. where postcode between 'N1%' and 'N19%'
   This is a bit more tricky. If you are using between, you are searching a range - and a range must have precised limits (eg from 1 to 5). Ranges of strings must have precise limits too, so you say:-
   where postcode between 'N1' and 'N19'

6. select urn
   from pledges
   where update_date > date('today') -'6 months'
   OK, trick question. There's nothing wrong with this selection as such - but it will list all the people who have paid pledges in the last 6 months, even if the pledge has subsequently been deleted. If you want to exclude pledges which are deleted, add the following SQL:-
   and pledge_status != 'D'

7. select urn
   from mailable_members
   where raffles = 'N'
   or country_code = 'SO'
   and payments_per_year = 12
   
   How will this be interpreted? As:-
   where raffles = 'N'
   or (country_code = 'SO'
   and payments_per_year = 12)
   
   or maybe:-
   where (raffles = 'N'
   or country_code = 'SO')
   and payments_per_year = 12
   
   This is a real example. Never leave it to chance - always put in brackets to make your meaning clear. The person who made this error ended up working for Greenpeace...