Before we go further, can you tell us which assembler you're working in? There are significant differences in how different assemblers handles structures.
Also, if you're working in linked lists, we'll also need to know the operating system, as you'll need to use the system calls for memory allocation and deleting.
This thread may help you understand how structures in assembly work, though it uses a specific assembler/emulator (SPIM, a MIPS emulator) for its examples; more advanced assemblers such as MASM and Netwide Assembler have built-in support for structures that is comparable to languages such as C.
OK, then. Assuming that we're talking about 16-bit code, a simple linked list node in MASM might look like this:
data WORD ?
next WORD ?
Of course, the structure itself isn't the only important factor; it's how you use it that counts. The structure is more or less a template or pattern for a particular interpretation of a block of memory. In the case of a linked list, generally speaking this memory will be allocated at run time from the operating system.