I want to take admission in DU for the course of LL.B after graduation, suggest me a book for the entrance exam 2019

Hi there.
For DULLB preparation all you need is one book that is Universal's Guide to CLAT & LLB Entrance examinations.
I know this sounds pretty unbelievable but trust me this book is your only need. With more than 11000 Multiple Choice questions, it has previous years questions of DULLB as well as other law entrance examinations. Not just that, it even has mock test papers. This is your one step solution for law entrance examination preparation.
With so many questions to brush up your knowledge, it also includes the whole syllabus of DULLB and other law entrance examinations. From General Knowledge, to Legal Aptitude, to Logical Reasoning, even English! Everything is there in this book.
You wouldn't have to touch other books if you follow this one.
Other than that, you can also refer Lakshmikant's Indian Polity and NCERT textbooks of History, Geography, and Political Science for basic preparation. Make a habit of reading newspaper daily, for this purpose, "The Hindu" is highly recommended. You may also follow Yojana Magazines for current affairs.
Keep a watch on news, using social media and Television to be successfully updated with current affairs.
P.S : Reading would increase your vocabulary. For budding lawyers, "10 judgements that changed India" by Zia Mody and "Legal Eagles" by Indu Bhan are great books. They are not specified for CLAT preparation but will help you a lot in your journey of becoming an advocate.
Hope this helps.
Good luck!