Question

When I went to my friend’s house, he _____. (fill past continuous form of sleep)​

Answer 1

when i went to my friend’s house, he was sheeping .

Answer 2

When I went to my friend's house, he was sleeping.

A quick FYI :

Past continuous (progressive) tense for sleep is:

• For "He, She and It" ---» was sleeping.
• For "we, you and they" ---» were sleeping.

That is, for a singular, the past continuous tense is "was sleeping" and for a plural, it is "were sleeping".