It's unclear exactly what this session was for. My theory is that these photos were taken in the first or second week of March 1969 and John is listening to tapes for Unfinished Music No. 2: Life With The Lions. More specifically, I would guess he's listening to "Cambridge 1969". Here's my theory...
1. John's attire was typical for late 1968 through early 1969. He is seen wearing the jean jacket during the later "White Album" Sessions, at the Rock and Roll Circus sessions in December 1968 and during the "Get Back" sessions in January 1969. Starting in March 1969, he was typically seen more formally dressed. Usually in his white suit.
2. John started growing his first beard in early February 1969. His beard is reasonably established in these photos. See additional discussion regarding The Beatles' facial hair at the "Mystery Session". Additionally, once John began his "formal" look in late March 1969, his beard had become much fuller and his hair more frizzy and remained so until he cut it short in early 1970. This would place the date of the photos sometime between 15 Fabruary and 20 March 1969.
3. In November 1968 John made recordings during Yoko's stay at Queen Charlotte's Maternity Hospital. The recordings were utilized for two different releases. The first release was the Aspen 7 box (see details - here). This was prepared by Malcolm Davies in late January 1969. According to Mark Lewisohn, on 11 February 1969, John and Yoko remixed mono tapes for mock-stereo at E.M.I. Studios. John Winn, in That Magic Feeling, states that these mixes were released on Unfinished Music No. 2: Life With The Lions.
4. On 2 March 1969, John and Yoko performed live at Lady Mitchell Hall in Cambridge. The performance was recorded and released as "Cambridge 1969" on Unfinished Music No. 2: Life With The Lions.
5. Lewison also notes that, on 12 March 1969 John and Yoko were at E.M.I. "listening to a playback of a privately recorded tape which was named "Peace Song" on the EMI log sheet". To date, this recording has not surfaced.
6. Based on the recording equipment, this session would have to be after the Apple Studio re-build. In addition, John Barrett's notes document a tape reel numbered E65786 with the description 4T New Mixer Tape (90% TEST TONE - A LITTLE OF "I WANT YOU") 24 Feb 1969. This would inticate that 4-track equipment was installed during the re-build. This would certainly also include 2-track mixdown equipment. The tape machine seen in the photos is either 2 or 4 track (it's not 8-track). It has also been noted that, initially, the new Apple equipment was problematic. In the photos, the equipment would appear to be operating properly.
These photos might be relative to any of the items listed above but my theory is that this is likely a mixing or playback session for "Cambridge 1969". This performance, considering its content, would seem to be something that John might to prefer to mix at Apple. Additionally, unlike E.M.I., Apple is notorious for a lack of documentation which could be why no E.M.I. documentation has surfaced.
In one of the photos, which was surely taken at the same time, John is seen at the piano but this could have been for photo purposes or he was possibly simply killing time.
According to photographer, Tom Hanley, "The recording studio in the basement of the Apple office at 3 Saville Row in London was only used by the Beatles together for some of the Get Back recording sessions in early January 1969. Some of their other protégé artists and groups rehearsed down there. John is seen here using the editing suite. The Beatles only rarely came together in the office during 1969."
"During 1969 I was privileged and free to walk in and out the Apple office at will and take pictures of who and whatever. But the Beatles themselves appeared very little and never together. I knew of the problems going on between them but still hoped, (as we all did) that they would come together again. This afternoon John was editing some tapes in the basement, you always knew where you stood with him, whether to stay and take pictures or get out of the way."
Phil McDonald sets up a playback as Glyn Johns looks on. Yoko looks quite bored.