Is there a canon timeline to CLAMP works? I keep reading that alot of CLAMP's works are set in encompassing universe kinda like TYPE-MOON's Nasuverse particularly how Yūko in xxxHolic seems to interact with Syaoran from Tsubasa Chronicle and has some sort of relationship with Clow Reed, the sorcerer who created the Clow Cards in Cardcaptor Sakura. also Tsubasa Chronicle seems to cross into X/1999 at one point.

I am wondering, are there canon timelines for watching/reading CLAMP Material? an example from the Nasuverse would be Mahou Tsukai no Yoru -> Fate/Zero -> Tsukihime -> Fate/Stay Night -> Fate/Hollow Ataraxia -> Alliance of Illusionary Eyes -> Kagetsu Tohya -> Melty Blood
To combine them all to be one timeline like the one you shared... I'm not sure, because many cameo appearances indicate they're in the same timeline, and Clamp has many titles... So, for Clamp timeline, I suggest see this Wikipedia: List of Clamp Works. Use the list of Completed Works, read just like how it's ordered there, but:


put Kobato before Tsubasa: Reservoir Chronicle, because there's Kobato characters appear in TRC.
put Gohou Drug between Suki, Dakara Suki and Chobits, because Hina of Suki, Dakara Suki make appearance as cameo in Gohou Drug
put X between Clamp School Detectives and Duklyon, because, when the main characters in Duklyon watch a movie in cinema, the movie they watch is... X.
exclude Clamp no Kiseki (not a manga), Watashi no Suki na Hito (more of an essay), and Shirahime-Syo (manga, but so far it has no relation at all with other series). 
nah, for whether to XXXHolic or TRC first... it's very hard because they had parallel storyline. You could see this thread in MAL discuss which one comes first, but actually as far as I know, they're parallel.


Deeper:

Some that I know from reading the manga itself or from source in the bottom, but the problem is that I have bad memory, so I can't give the exact chapter.

x -> y: y comes after x
x &lt;-> y: parallel (same timeline)

Cardcaptor Sakura -> XXXHolic &lt;-> Tsubasa Reservoir Chronicle


   Just a you've said, XXXHolic's characters make appearance in TRC, vice versa, but judging from the plot, they're parallel. Why Cardcaptor Sakura first, because it tells Sakura and Syaoran's childhood, while in TRC they were married. 


Angelic Layer -> Chobits


   The inventor of Chobits and Angelic Layer is the same, Icchan. Chitose is his wife. Why Angelic Layer first, because in Angelic Layer Icchan lived and he has died at Chobits.


Tokyo Babylon, Clamp Detective School -> X


   Sumeragi and Sakurazuka clan is involved with the end of the world in X. Why Tokyo Babylon first, because it could be said that Tokyo Babylon is the story of Subaru, Hokuto,  and Sakurazukamori when they're younger, and Hokuto's still alive, since in X she has died. Nokoru, Suou, and Akira made appearance in X as cameo, and they're adult there.


20 Mensou ni Onegai!! &lt;-> Clamp School Detectives &lt;-> Duklyon: Clamp School Defenders 


   All in the same timeline and set in the same background, Clamp School. Nokoru appears in Duklyon as their commanders (well actually someone with blackglass, but that hair, appearance, position, and personality is undeniably Nokoru), Akira and Utako is the main character of 20 Mensou, and those Duklyon defenders made cameo appearance in Clamp School Detectives. 


Many Clamp's work except CCS and XXXHolic -> Tsubasa: Reservoir Chronicle

Many of Clamp's chara appear in TRC, but they appears as their parallel counterpart, thus have nothing to do with the original story, and even if you haven't read it, it's fine.

Source:
TRC Wikia: The list of other series appearance in TRC
Y!A: Clamp manga set in the same universe

CMMIW. To tell the truth, I just shared what I know.