For the second sentence, "the end" is translated into Korean as "끝" or "마지막" but, the translated sentence in above answer "끝내는 것 같아요." sounds a bit weird. I suggest that you can say it as - I think this is the end = (I think 제 생각엔) 이것이 마지막(or 끝)인 것 같아요. Also, for the last one, it is better to translate it as below I think this book is very interesting = (I think 제 생각엔) 이 책은 아주 흥미로워요.

I think my friend will come tomorrow = 내 친구가 내일 올것 같아요. i think this is the end = 끝내는 것 같아요 i think this book is very interesting = 그 책이 재미있는 것 같아요 For the second sentence, the word "end" can be different in korean. It depends of what u're talking about. Maybe a native will be better than me ^^