Its almost 6 months, since the comment form was taken out of Blogger in draft and made available for all Blogger users. This was considered to be a major update for Blogger, towards it is move to be a professional blogging platform just like WordPress .

If you haven’t added comment form in your Blogger posts , Just follow these steps .Open your Blogger blogs settings and select comments from tabs .There you will see many options .
1.Select the radio button to show comments -This action will display all comments in your Blog .
2.Who Can Comment? :Select the type of users who can comment .
3.Comment Form Placement :At this point , select to embed comment form below posts .
There are other options , but comment form below Blogger posts normally looks professional .Still if you can’t see a comment form below your Blogger posts ,Find the following section .

<p class='comment-footer'> <b:if cond='data:post.allowComments'> <a expr:href='data:post.addCommentUrl' expr:onclick='data:post.addCommentOnclick'><data:postCommentMsg/></a> </b:if> </p>

Replace it with this one .

<p class='comment-footer'> <b:if cond='data:post.embedCommentForm'> <b:include data='post' name='comment-form'/> <b:else/> <b:if cond='data:post.allowComments'> <a expr:href='data:post.addCommentUrl' expr:onclick='data:post.addCommentOnclick'><data:postCommentMsg/></a> </b:if> </b:if> </p>

And save your Blogger template .4.Towards the end ,you will see other comment form options like comment form message , comment notification and comment moderation . Comment form messages appears just above the comment form box. Enable comment moderation , if you want to moderate comments before they appear in your posts.