How can I find all files I do not have write access to in specific folder?

Try

find . ! -writable

the command find returns a list of files, -writable filters only the ones you have write permission to, and the ! inverts the filter.

You can add -type f if you want to ignore the directories and other 'special files'.

On non-Linux systems and systems without GNU find, the following is likely to give the same output as find . -type f ! -writable, it does however not take secondary groups into account.

myname=$( id -un )
mygroup=$( id -gn )

find . -type f '(' \
       '('   -user "$myname"                     ! -perm -u=w ')' -o \
       '(' ! -user "$myname"   -group "$mygroup" ! -perm -g=w ')' -o \
       '(' ! -user "$myname" ! -group "$mygroup" ! -perm -o=w ')' ')'

The four tests in order:

1. Is it a regular file?
2. Is it a file that I own but that I don't have write permissions to?
3. Is it a file that I don't own, but that belongs to my group, and that I don't have group write permissions to?
4. Is it a file that I don't own and that does not belong to my group, and that I don't have general ("other") write permissions to?

The benefit of this is that you may substitute in another user's name and group, which I don't think GNU find's -writable allows you to do.

---

The same command but with the logic written in AND form:

find . -type f \
    ! '('   -user "$myname"                     -perm -u=w ')' \
    ! '(' ! -user "$myname"   -group "$mygroup" -perm -g=w ')' \
    ! '(' ! -user "$myname" ! -group "$mygroup" -perm -o=w ')'