We know that the top 3 runs scorers in Tests in 2023 are:
Khawaja 1,168
Head 902
SPD BradSmith 853.
Special K's effort is all the more meritorious because he has scored those runs from just 2 home Tests and 10 away Tests, all against very strong opposition (4 in India and 6 in England, one of which was the Test Championship Final against India).
Against each nation, the highest-scorers are:
Against Afghanistan - Najmul Hossain Shanto (Bangladesh) - 270 runs (Mominul Haque 136)
Against Australia - Crawley (Eng) 480 (Root 412)
Against Bangladesh - Phillips (NZ) - 181 (Tucker [Ire] 145)
Against England - Khawaja (Aus) - 496 (SPD BradSmith 373)
Against India - Head (Aust) 416 - (Khawaja 346)
Against Ireland - Mendis (SL) 385 (Karunaratne 294)
Against New Zealand - Brook (Eng) 329 (Root 319)
Against Pakistan - de Silva (SL) 271 (Warner 164)
Against South Africa - Khawaja (Aus) 195* (Blackwood 126)
Against Sri Lanka - Williamson (NZ) 337 (Shakeel 295)
Against West Indies - Markram (SA) 276 (Jaiswal 266)
Against Zimbabwe - Chanderpaul (WI) 258 (Brathwaite 214).