PS

*bi/ark- - knee (SED I No. 39)

Cf. *rVk(u)b(­at)­ ‘knee’ (No. 232) and discussion in [GD 163], where separation of these two roots is also favored.

Akkadian
birku, burku - knee, lap (CAD B 255, AHw. 129)
-­u-­ in Akk. (alongside with ­-i-­) and Arm. (Syr. and Mnd.) is likely a secondary development under the influence of b-­. For the meaning ‘lap’, see *barak-­ ‘chest, thorax’. See discussion in [Holma 1911 95] where the author tends to treat birku ‘knee’ and birku ‘genitals’ as the same word, quoting, at the same time, Arb. rakab-­ ‘pubis’ as a possible cognate to the latter.
Ugaritic
brk - knee (DUL 237)
Hebrew
bäräk - knee (HALOT 160)
bäräk (< *bark-­; suff. birk-­). Note Hbr. pB. bōräk ‘knee-shaped shaft of a plough’ [ibid.].
Biblical Aramaic
birkōhī - (du. suff. 3ms) knee (HALOT 1839)
Jewish Palestinian Aramaic
brkh - knee (DJPA 114)
du. bärkayin
Jewish Babylonian Aramaic
birkā - knee (DJBA 206)
Syriac
burkā - knee; bowing down, genuflection; middle part of plow (LSyr. 96, SL 131)
Mandaic
burka - knee (MD 57)
Mlaḥso
berko - Knie (knee) (Jastrow 1994: 170)
Turoyo
barko - Knie (knee) (RW 56)
Barwar
bǝrka - knee (Khan 2008: 1248)
Hertevin
berka - Knie (knee) (Jastrow 1988: 183)
Arabic
bārikat-­ - to kneel (Lane 193, BK 1 116)
Formed after the active participle pattern; strangely enough, usually not quoted in comparative studies (see [DRS], [LGz]). Cf. also brk ‘s’agenouiller’ [BK 1 116]. As for bark­-, birk­- ‘genou’ quoted in [GD 153], it is not clear whether it is Daṯ. or Mhr.
Geez
bərk - knee (CDG 105)
Tigre
bərək - knee (WTS 278)
Tigrinya
bərki - knee (TED 1125)
Harari
bərḫi - the unit between two joints (in a finger, sugar cane) (EDH 45)
Selti
bərk - knee (EDG 153)
Wolane
bərk - knee (EDG 153)
Mehri
bark - knee (ML 52)
Jibbali
bɛrk - knee (JL 28)
Harsusi
bark - knee (HL 19)