This part deals with the present wishful thinking of someone about how good/happy it would have been to have/possess something in the past though actually they didn’t possess it. Or in other words it refers the present wishful thinking of someone about an unsuccessful desire to have or possess something in the past.

• She wishes she had had a post graduation in Science. (but she didn’t have a PG)
• She wishes she had had long beautiful hair. (but unfortunately she didn’t have it)
• The Headmistress wishes the school had had a beautiful garden. (but the school didn’t have a …)
• John wishes he had had a motorbike. (but he didn’t have a ….)
• The poor man wishes he had had a house of his own. (but unfortunately he didn’t have…)
• I wish I had had a car. (but I didn’t have a car)
• I wish I had had enough money to help you. (i.e. I didn’t have enough money to help you)

Note: The past perfect form of ‘Had’ is ‘Had Had’.  Thus the sequence of tense will be like:

Has or Have — Had — Had Had