First of all, you cannot say "o dedin" OR "o dedin ki" in Turkish. This form could be used for singular you. "Sen dedin" or just "dedin (you)". -ki is a bit complex suffix. You can use it with several verbs to give a meaning like "I've already done it". For example; Mom: "Ödevini yap! (Do your homework!)" Son: "Yaptım ki." (Literally means I've already done it). But, while using the verb demek (to say), it means that a sentence will follow the verb. For instance; "Onu aradım ve dedim ki: 'Yarın gelmeni istemiyorum'". (I called him and said (that): 'I don't want you to come tomorrow'". Here "dedim ki"="I said (that)"

I hope this e-book will help you. https://books.google.com.tr/books?id=7fXCKZmee8QC&pg=PA463&lpg=PA464&dq=There+are+three+type+%E2%80%9Cki%E2%80%9D+in+Turkish.&source=bl&ots=yfGRGHO88l&sig=Jg-QBH5nZBDA_7wjLOClp54Vty8&hl=tr&sa=X&ved=0ahUKEwj8ksCszKzLAhVLjiwKHW_qC-oQ6AEIJTAB#v=onepage&q=There%20are%20three%20type%20%E2%80%9Cki%E2%80%9D%20in%20Turkish.&f=false

First of all, you cannot say "o dedin" OR "o dedin ki" in Turkish. This form could be used for singular you. "Sen dedin" or just "dedin (you)". -ki is a bit complex suffix. You can use it with several verbs to give a meaning like "I've already done it". For example; Mom: "Ödevini yap! (Do your homework!)" Son: "Yaptım ki." (Literally means I've already done it). But, while using the verb demek (to say), it means that a sentence will follow the verb. For instance; "Onu aradım ve dedim ki: 'Yarın gelmeni istemiyorum'". (I called him and said (that): 'I don't want you to come tomorrow'". Here "dedim ki"="I said (that)"