What is a Huffman tree for a Block-Code? We have the word "w = aabceefgeebdaabbceeffghdcbbeefbbbbghhie ".  

I have created a Huffman tree for the string w. 

We get the following table: 



Now I want to create a Huffman tree for a Block-Code with length of block $4$. 

Do we maybe take each consecutive 4 letters, i.e., {aabc, eefg, eebd, aabb, ceef, fghd, cbbe, efbb, bbgh, hie} to make the tree? 

But then the last one is of length 3 and not 4.  

So, do we choose in an other way the blocks?
In your context, a block code of length $\ell$ encodes $\ell$ letters at a time. The domain thus consists of all words over the alphabet of length $\ell$. Unless you're told otherwise, the assumption is that the individual letters are independent - the probability of a word $\sigma_1 \dots \sigma_\ell$ is the product of the probabilities of the individual letters.