You might want to check out This Website for that information. According to thier information, the ship was taking on coal at the bay of Rio de Oro in West Africa when she was confronted by the HMS Highflyer.
I actually saw one of the bells of Kaiser Wilhelm der Grosse a mere few hours ago which is on display at the Wissenschaftliches Institut fí¼r Schiffahrts- und Marinegeschichte (Scientific Institute of Shipping- and Naval History) in Hamburg. It is quite a piece! Most of the valuable fittings of the ship were dismantled before she was turned into an armed merchant cruiser. The First Class Smoke Room also still exists and is on display at the Deutsches Schiffahrtsmuseum in Bremerhaven. I have only seen pictures of it though. It is said the wreckage of Kaiser Wilhelm der Grosse was still visible in the 1950s when her remains were scrapped as she was declared a shipping hazard. You might want to check out the german model ship journal ModellWerft from September 2001 in which is the start of a two part series about the liner that I wrote, which also describes my experiences of building a model of this ship.
There were in fact five german four stackers. The first was of course the Kaiser Wilhelm der Grosse. Her sister ship was the Kronprinz Wilhelm. They were more or less identical, though the Kronprinz Wilhelm didn't have bridge wing cabs. I think they were both Blue Ribband holders. Later on the North German Lloyd commissioned two further four stackers the Kaiser Wilhelm II and the Kronprinzessin Cecilie. These were also sisterships but very different to the first two as the later ships had two promenade decks and were larger than the first.
Hamburg Amerika Line also wanted their share and commissioned the Deutschland which would also capture the Blue Ribband. However she vibrated heavily at high speeds and was taken off the north Atlantic run later and renamed Victoria Luise used as a cruise ship.
The following is largely abstracted from an article in Sea Breezes, October 1996 (the copyright resides with myself):
Kaiser Wilhelm der Grosse was launched from the Vulcan yard at Stettin on May 3rd 1897. She was registered at Bremen. Her maiden voyage was from Bremen on September 19th 1897.
On her third voyage, under the command of Kapitän Engelbart, end of passage at The Needles, 3.10 p.m. November 29th 1897 put her on record as the world's largest and fastest passenger vessel.
In 1900 an experimental Marconi installation was put aboard.
On June 30th 1900 she narrowly escaped destruction when fire swept through the Norddeutscher Lloyd appropriated piers at Hoboken, New Jersey.
On November 23rd 1906 she collided with the Orinoco (Royal Mail Steam Packet Company) off Cherbourg with fatalities on both vessels. KWDG was subsequently held 100% to blame.
On October 25th 1907 her rudder carried away in heavy weather and she completed the remainder of an eastbound passage steering by her twin screws only.
On the outbreak of hostilities in 1914 she was requisitioned by the Imperial German Navy as an armed merchant cruiser. She was painted black overall and was fitted out with six 10.5 cm guns and two 3.7 cm cannon.
Her first and only cruise as a warship commenced from Bremerhaven on August 4th 1914 under the command of Kapitän Reymann. She encountered and sank the steam trawler Tubal Cain. She then encountered the Arlanza (Royal Mail) and the Galician (Union Castle) but allowed these vessels to proceed because they had large passenger complements. She later sank the Kaipara (N.Z.S.Co.) and the Nyanza (Elder Dempster), taking their crews prisoner.
She later rendezvous'd with four bunkering and provisioning vessels (Duala, Aruca, Magdeburg and Bethania) at Villa Cisneros, Rio de Oro in what were then Spanish colonial waters. She found herself blockaded at her anchorage by the cruiser HMS Highflyer (Captain Buller). Captain Buller held KWDG to be in contravention of the Hague Conventions of 1907 by failing to clear neutral waters within the stipulated time limit.
His call for surrender was refused. Kapitän Reymann sent away his prisoners in the Aruca and some 400 surplus crew members in the Bethania.
Highflyer eventually moved in and opened an engagement with gunfire. The German guns had the greater range and initially Highflyer sustained damage to her signal platform with one crew member killed. However, KWDG eventually succumbed to the British cruiser's heavier firepower and she foundered at 5.10 p.m. on August 10th 1914. Some reports say she was scuttled.
Kapitän Reymann, 9 officers and 71 surviving crew escaped to the shore. Here they took up hostile positions among the dunes, still refusing to surrender. Highflyer withdrew, her commander being mindful of Spanish neutrality and satisfied that he had achieved his principal objective of taking out this threat to Allied shipping.
The marooned German shore party then petitioned for asylum to the Spanish garrison at the nearby fort. They were interned for the duration, later being transferred to three German vessels already under detention at Las Palmas de Gran Canaria. Some later escaped and made it back to Germany.
The Aruca landed her prisoners at Las Palmas. Bethania, with the 400 transferred crew members, got clear but was later brought into Kingston, Jamaica by HMS Essex.
I understood that the wreck of KWDG was shown on charts 3251 2078 (Nov 1982) (Bahia de Villa Cisneros) and 3134 1690 (May 1993) (Approaches to Ad Dakhla and Ad Dakhla). At the time of my research Ad Dakhla was in Western Sahara, a territory in dispute between Mauritania and Morocco and latterly under the military control of Morocco.
My research did not extend to whether any salvage work had been done on the wreck and, as I write, I cannot say if it appears on the current charts after the reported salvage work.
The PRO references are:
ADM137/799 p.167 Capt. Buller to Admiralty, Secret (account of the engagement) also p.135 (Capt.C.E.Down, Arlanza, Royal Mail Steam Packet Company, to owners August 22nd 1917; forwarded to Admiralty for info.)