The design is the visual features of the FREESTANDING WORKSPACE ENCLOSURE as shown in the drawings, whether those features are features of one of shape, configuration, ornament or pattern or are a combination of any of these features. Drawing of the design are included. In the drawings: Fig. 1 is a front perspective view of a FREESTANDING WORKSPACE ENCLOSURE in accordance with a first variant of said Industrial Design; Fig. 2 is a top view of the FREESTANDING WORKSPACE ENCLOSURE of Fig. 1; Fig. 3 is cross-sectional view of the FREESTANDING WORKSPACE ENCLOSURE of Fig. 1 through section 3-3 shown in Fig. 1; Fig. 4 is a front view of the FREESTANDING WORKSPACE ENCLOSURE of Fig. 1; Fig. 5 is a rear view of the FREESTANDING WORKSPACE ENCLOSURE of Fig. 1; Fig. 6 is a right side view of the FREESTANDING WORKSPACE ENCLOSURE of Fig. 1, with the left side view being a mirror image; Fig. 7 is a front perspective view of a FREESTANDING WORKSPACE ENCLOSURE in accordance with a second variant of said Industrial Design; Fig. 8 is a top view of the FREESTANDING WORKSPACE ENCLOSURE of Fig. 7; Fig. 9 is cross-sectional view of the FREESTANDING WORKSPACE ENCLOSURE of Fig. 7 through section 9-9 shown in Fig. 7; Fig. 10 is a front view of the FREESTANDING WORKSPACE ENCLOSURE of Fig. 7; Fig. 11 is a rear view of the FREESTANDING WORKSPACE ENCLOSURE of Fig. 7; Fig. 12 is a right side view of the FREESTANDING WORKSPACE ENCLOSURE of Fig. 7, with the left side view being a mirror image; Fig. 13 is a front perspective view of a FREESTANDING WORKSPACE ENCLOSURE in accordance with a third variant of said Industrial Design; Fig. 14 is a top view of the FREESTANDING WORKSPACE ENCLOSURE of Fig. 13; Fig. 15 is cross-sectional view of the FREESTANDING WORKSPACE ENCLOSURE of Fig. 13 through section 15-15 shown in Fig. 13; Fig. 16 is a front view of the FREESTANDING WORKSPACE ENCLOSURE of Fig. 13; Fig. 17 is a rear view of the FREESTANDING WORKSPACE ENCLOSURE of Fig. 13; Fig. 18 is a right side view of the FREESTANDING WORKSPACE ENCLOSURE of Fig. 13, with the left side view being a mirror image; Fig. 19 is a front perspective view of a FREESTANDING WORKSPACE ENCLOSURE in accordance with a fourth variant of said Industrial Design; Fig. 20 is a top view of the FREESTANDING WORKSPACE ENCLOSURE of Fig. 19; Fig. 21 is cross-sectional view of the FREESTANDING WORKSPACE ENCLOSURE of Fig. 19 through section 21-21 shown in Fig. 19; Fig. 22 is a front view of the FREESTANDING WORKSPACE ENCLOSURE of Fig. 19; Fig. 23 is a rear view of the FREESTANDING WORKSPACE ENCLOSURE of Fig. 19; Fig. 24 is a right side view of the FREESTANDING WORKSPACE ENCLOSURE of Fig. 19, with the left side view being a mirror image; Fig. 25 is a front perspective view of a FREESTANDING WORKSPACE ENCLOSURE in accordance with a fifth variant of said Industrial Design; Fig. 26 is a top view of the FREESTANDING WORKSPACE ENCLOSURE of Fig. 25; Fig. 27 is cross-sectional view of the FREESTANDING WORKSPACE ENCLOSURE of Fig. 25 through section 27-27 shown in Fig. 25; Fig. 28 is a front right view of the FREESTANDING WORKSPACE ENCLOSURE of Fig. 25; Fig. 28A is a front left view of the FREESTANDING WORKSPACE ENCLOSURE of Fig. 25; Fig. 29 is a rear right view of the FREESTANDING WORKSPACE ENCLOSURE of Fig. 25; Fig. 30 is a rear left view of the FREESTANDING WORKSPACE ENCLOSURE of Fig. 25; Fig. 31 is a front perspective view of a FREESTANDING WORKSPACE ENCLOSURE in accordance with a sixth variant of said Industrial Design; Fig. 32 is a top view of the FREESTANDING WORKSPACE ENCLOSURE of Fig. 31; Fig. 33 is cross-sectional view of the FREESTANDING WORKSPACE ENCLOSURE of Fig. 31 through section 33-33 shown in Fig. 31; Fig. 34 is a front view of the FREESTANDING WORKSPACE ENCLOSURE of Fig. 31; Fig. 35 is a rear view of the FREESTANDING WORKSPACE ENCLOSURE of Fig. 31; and, Fig. 36 is a right side view of the FREESTANDING WORKSPACE ENCLOSURE of Fig. 31, with the left side view being a mirror image.