How to see what will be updated from repository before issuing "svn update" command?

Try:

svn status --show-updates

or (the same but shorter):

svn status -u

Depending on what you want to know between your working copy and the latest svn server repository, without updating your local working copy, here is what you can do:

if you want to know what has been changed in svn server repository, run command:

$ svn st -u

if you want to know if the same file has been modified both in your local working copy and in svn server repository, run command:

$ svn st -u | grep -E '^M {7}\*'

if you want to get list of files changed between a particular revision and HEAD, run command:

$ svn diff -r revisionNumber:HEAD --summarize

if you want to get a list of files changed between paticular revisions, run command:

$ svn diff -r revisionNumber:anotherRevisionNumber --summarize

if you want to see what will be updated (without actually updating), run command:

$ svn merge --dry-run -r BASE:HEAD .

if you want to know what content of a particular file has been changed in svn server repository compared with your working copy, run command:

$ svn diff -r BASE:HEAD ./pathToYour/file

if you want to know what contents of all the files have been changed in svn server repository compared with your working copy, run command:

$ svn diff -r BASE:HEAD .

You can see what will updated (without actually updating) by issuing:

svn merge --dry-run -r BASE:HEAD .

More details here.