Hi @Tom18 !
Accordint the Installation Guide (https://support.hpe.com/hpesc/public/docDisplay?docLocale=en_US&docId=a00070982en_us ) the HPE 5945 48SFP28 8QSFP28 switch provide two SFP ports on the rear panel. You can install JD089B there. Also, according the Installation Guide:
The HPE 5945 48SFP28 8QSFP28 switch provides 48 SFP28 ports. The LSWM124TG2H provides 24 SFP28 ports. The SFP28 ports support the following transceiver modules and cables:
• SFP28 transceiver modules in Table 28.
• SFP28 copper cables in Table 29.
• 10-GE SFP+ transceiver modules in Table 30.
• 10-GE SFP+ copper cables in Table 31.
• 10-GE SFP+ fiber cables in Table 32.
• GE SFP transceiver modules in Table 19.
Table 19 contains JD089B HPE X120 1G SFP RJ45 T Transceiver:

It means this transceiver can be used in any of the SFP28 ports available. But be aware that maybe you will need to use static speed and duplex, as auto-negotiation on SFP28 ports may not work with these transceivers. Just in case be prepared to configure 'speed 1000" and 'duplex full' on those ports if link won't go up.
Hope this helps!