The book is not interesting enough ______ my attention.

• Enough (যথেষ্ট) শব্দটি adjective ও adverb হিসেবে ব্যবহৃত হয়। 
- Adverb/adjective এর পর 'enough' বসলে to-infinitive (to + verb এর base form) ব্যবহৃত হয়।
Structure - adverb/adjective + enough + (to+verb+....) 
Example - He didn't run fast enough to win the race.

• আবার,
- adjective/adverb/verb + enough + for + pronoun (me/him/her, etc) + (to+verb) এরূপেও ব্যবহৃত হয়। 
Example - What he says is not clear enough for me to hear him clearly.

• প্রদত্ত sentence এ 'interesting' (adjective) এর পর 'enough' শব্দটি এসেছে।
- তাই to-infinitive (to + verb এর base form) ব্যবহৃত হবে।

Complete Sentence - The book is not interesting enough to hold my attention. 

Source: A Passage to the English Language by S.M. Zakir Hussain.