The Debian packaging of debug-me is maintained in git, using the
merging workflow described in dgit-maint-merge(7).  There isn't a
patch queue that can be represented as a quilt series.

A detailed breakdown of the changes is available from their canonical
representation - git commits in the packaging repository.  For
example, to see the changes made by the Debian maintainer in the first
upload of upstream version 1.2.3, you could use:

    % git clone https://git.dgit.debian.org/debug-me
    % cd debug-me
    % git log --oneline 1.2.3..debian/1.2.3-1 -- . ':!debian'

(If you have dgit, use `dgit clone debug-me`, rather than plain `git
clone`.)

A single combined diff, containing all the changes, follows.
--- debug-me-1.20190926.orig/Server.hs
+++ debug-me-1.20190926/Server.hs
@@ -16,7 +16,7 @@ import Log
 import Network.Wai
 import Network.Wai.Handler.Warp
 import Network.Wai.Handler.WebSockets
-import Network.WebSockets hiding (Message)
+import Network.WebSockets hiding (Message, serverPort)
 import qualified Network.WebSockets as WS
 import Network.HTTP.Types
 import Control.Concurrent
--- debug-me-1.20190926.orig/Val.hs
+++ debug-me-1.20190926/Val.hs
@@ -42,7 +42,7 @@ instance FromJSON Val where
 b64 :: B.ByteString -> T.Text
 b64 = T.decodeUtf8 . B64.encode
 
-unb64 :: Monad m => T.Text -> m B.ByteString
+unb64 :: MonadFail m => T.Text -> m B.ByteString
 unb64 t = either
 	(\_ -> fail "bad base64 data")
 	return
--- debug-me-1.20190926.orig/debug-me.cabal
+++ debug-me-1.20190926/debug-me.cabal
@@ -50,7 +50,7 @@ custom-setup
 
 Executable debug-me
   Main-Is: debug-me.hs
-  GHC-Options: -threaded -Wall -fno-warn-tabs -O2
+  GHC-Options: -threaded -Wall -fno-warn-tabs -O2 -XNoMonadFailDesugaring
   Build-Depends:
       base (>= 4.9 && < 5.0)
     , network (>= 2.6)
--- debug-me-1.20190926.orig/debug-me.init
+++ debug-me-1.20190926/debug-me.init
@@ -33,7 +33,7 @@ case "$1" in
 		start-stop-daemon --start --quiet --oknodo \
 			--background --no-close \
 			--pidfile "$PIDFILE" --make-pidfile \
-			--chuid debug-me:debug-me \
+			--chuid _debug-me:_debug-me \
 			--exec "$DAEMON" -- $DAEMON_PARAMS \
 			> /var/log/debug-me.log
 		log_end_msg $?
--- debug-me-1.20190926.orig/debug-me.service
+++ debug-me-1.20190926/debug-me.service
@@ -8,8 +8,8 @@ EnvironmentFile=-/etc/default/debug-me
 ExecStart=/usr/bin/debug-me $DAEMON_PARAMS
 InaccessiblePaths=/home /etc
 ReadWritePaths=/var/log/debug-me
-User=debug-me
-Group=debug-me
+User=_debug-me
+Group=_debug-me
 StandardInput=null
 StandardOutput=journal
 StandardError=journal