Indeed, books for boys on understanding feelings is such an under-served book market!! It shows how behind we are as a culture on valuing that boys need to be taught emotional & mental health skills as well. The more we prepare them when young, the better brothers, fathers, boyfriends, spouses, etc we'll be preparing for the future.
SOOO, to help answer this question, I spent some quite time researching on Amazon some books for boys on this topic & threw in a few of my own recommendations from my experience as a mother/professional. I did find a few good choices.
1) Understanding Myself, A Kid's Guide to Strong Emotions & Strong Feelings (I just purchased this one @ B & N w/a giftcard, haven't had a chance to look thru it completely but what I saw, looked really fantastic, & written for BOTH genders !)
2) 'The What To Do Guides For Kids' series by Dawn Huebner, also a great resource, I've given the 'worry one' away a lot.
3) 100 Things Guys Need to Know by William Zimmerman (written to preteen market)
4) A Boys Book of Daily Thoughts by Jordan Storeby, an 11 y/o!! The description sounds wonderful! I'm ordering a copy for my nephews asap!